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1. the N EWS e Book HVACR Service and Troubleshooting With The Professor Checking on Refrigerant Overcharge his chapter will discuss refrigerant overcharge The check sheet shown on this page depicts a refrigeration system with an over charge of refrigerant The system in this example is a low temperature HFC 134a refrigeration unit with a TXV receiver Refrigerant Overcharge Measured Values See the chart at right Compressor Discharge Temperature 240 S f Condenser Outlet Temperature 90 mptoms rr l Evaporator Outlet Temperature T5 Symptoms can include e High discharge temperature Compressor In Temperature ZD e High condenser subcooling Ambient Temperature 70 e High condensing pressures e Higher condenser splits Bos Veli dette ne e Normal to high evaporator pressures Compressor Volts 230 e Normal superheats Compressor Amps High e High compression ratio High Discharge Temperatures With an overcharged system the high L E EPOE e AF Sile 2 compressor superheated vapor discharge temperature of 240 is caused from High Side Evaporating Pressure PSIG 172101200 the high compression ratio A discharge temperature of 225 250 is considered the maximum discharge temperature in order to prevent system breakdown Calculated Values F from excessive heat Liquid backed up in the condenser from the overcharge of refrigerant will flood some of the condenser s internal volume a
2. Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Figure 3 left The splitting of the condensers is done with the addition of a pilot operated three way solenoid valve installed in the discharge line from the compressors turers do supply technical information on how much extra refrigerant is needed for flooding a condenser for a certain low ambient condition However in extreme low ambient conditions it may be neces sary to flood 80 to 90 percent of the condenser On larger systems this could mean several hundred pounds of refrigerant This is the main disadvantage of flooding a condenser for low ambient operations With the rising price of refrigerant and the environmental concerns of global warming and ozone depletion condenser flooding can become guite expensive and environmentally unsound if not managed and serviced properly denser is referred to as the summer condenser Figure 2 The three way solenoid valve controlling the splitting of the condensers can be energized and de energized by a controller sensing outside ambient conditions an outdoor thermostat or a high side pressure control During summertime operations the added surface area and vol ume of both condensers are needed to maintain a reasonable head pressure at higher ambient conditions The pilot operated three way solenoid valve is then de energized This positions the main piston inside the valve to let refrige
3. Table 3 shows 40 of condenser subcooling but these amounts will vary depending on the amount of air in the system Again in this example high condenser subcooling is not caused from an amount of liquid being backed up in the condenser but from the liquid in the condenser s bottom simply losing heat faster ke Book HVACR Service and Troubleshooting With The Professor Table 3 System Containing Air Item to be measured Measured value Compressor discharge temperature 235 Condenser outlet temperature 65 i Evaporator outlet temperature Ly F Compressor inlet temperature 40 F Ambient temperature ZS Box temperature 15 F Compressor volts 230 V Compressor amps High Low side evaporator pressure 8 6 psig 5 F High side condensing pressure 185 5 psig 250 Item to be calculated Calculated value Condenser split S0 Condenser subcooling 40 F Evaporator superheat 12 Compressor superheat 25 F www z com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Megohmmeters for Preventive Maintenance egohmmeters meggers are electrical meters used to check the resistance and condition of the motor windings and the condition of the refrigeration and oil environment around the motor windings A megger is nothing but a gi ant ohmmeter that creates a very large dc voltage usually 500 volts dc from its internal battery The meter will read out in megohms millions of ohms Any motor w
4. Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor levels Otherwise the HCFC or HFC refrigerant trace gas vented along with the nitrogen will be considered a refrigerant This will constitute a violation of the prohibition on venting Also the use of CFC as a trace gas is not permitted 3 Temperature dependent leaks Temperature dependent leaks are associated with the heat of expansion They usually occur from high temper ature ambient air condenser blockages or during a defrost period 4 Vibration dependent leaks Vibration dependent leaks only occur during unit operation The mechanical stain of motion rotation refrigerant flow or valve actuation are all associated with vibration dependent leaks 5 Combination dependent leaks Combination dependent leaks are flaws that require two or more conditions in order to induce leakage For ex ample temperature vibration and pressure cause the discharge manifold on a semi hermetic compressor to expand and seep gas 6 Cumulative microleaks Cumulative microleaks are all the individual leaks that are too small to detect with standard tools The total refriger ant loss over many years of operation slightly reduces the initial refrigerant charge A system having many fittings welds seams or gasket flanges will probably have a greater amount of cumulative microleaks Spotting Refrigerant Oil Residue for Standing Leaks Successful leak detection is solely dep
5. and Troubleshooting With The Professor Restricted Metering Device Measured Values Compressor discharge temperature Condenser outlet temperature cccccccseccsescccsesceeesceeees 70 Evaporator outlet temperature Compressor in temperature Ambient temperature Box temperature Compressor volts Compressor amps 1 8 psig 10 104 2 psig 85 Low side evaporating pressure psig High side condensing pressure psig Calculated Values F Condenser split Condenser subcooling Evaporator superheat Compressor superheat Table 1 This is a system checklist for a system with a restricted metering device www PE ue com Y fink the High superheats High superheats are caused again from the evaporator and compressor being starved of re frigerant With the TXV restricted the evaporator will become inactive and run high superheat This will cause the compressor superheat to be high The 100 percent saturated vapor point in the evaporator will climb up the evapo rator coil causing high superheats Low amp draw High compressor superheats and low suction pressures will cause low density vapors to enter the compressor Also the compressor will be partly starved from the TXV be ing restricted These factors will put a A system with a restricted metering device has the very same symptoms as a system with a liquid line restriction that occurred after the receiver This is because the TXV is
6. converses with the two homeowners for about 10 minutes trying to get as much information and history about the a c problem as possible The technician then goes outside to the condensing unit and installs both of his gauges He instantly notices that the suction pressure is reading 50 psig 26 The normal suction pressure should be about 70 psig 41 for the outdoor tem perature and humidity conditions that day The head pressure is also low at 190 psig for the 90 day The head pressure should be in the 255 265 psig range The technician also notices the compressor sweating heavily from top to bottom The technician then touches the crankcase area or bottom to the compres sor and finds that it is extremely cold This means that the compressor has been suffering from liquid floodback during the day at some point during its Compressor in Temperature 28 F Saturated Evaporating Temperature 26 F Compressor Superheat OF Equation 1 run cycle Floodback is liquid refrigerant entering the crankcase of the com pressor during the running cycle The technician then installs a temperature probe on the suction line about 6 inches from where it enters the compres sor The temperature reads 28 The technician then subtracts the saturated evaporating temperature of 26 from the compressor inlet temperature 28 and finds out that there is only 2 of compressor superheat See Equation 1 This reinfor
7. system correctly www ze com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Refrigerant Migration efrigerant migration is defined as refrigerant either liguid or vapor traveling to the compressor s suction line or crankcase during the off cycle During the off cycle or especially during a long shutdown refrigerant will want to travel or migrate to a place where the pressure is the lowest In nature most fluids travel from a place of higher pressure to a place of lower pressure The crankcase usually has a lower pressure than the evapora tor because of the oil it contains Oil has a very low vapor pressure and re frigerant will flow to it whether the refrigerant is in the vapor or liquid form In fact refrigerant oil has such a very low vapor pressure it will not vaporize even when a 100 micron vacuum is pulled on the refrigeration system Some refrigeration oils have a vapor pressure of as low as 10 microns If the oil did not have a very low vapor pressure it would vaporize every time a low pressure exists in the crankcase or a vacuum was pulled on it If refrigerant migration does occur and the crankcase is lucky enough to have a crankcase heater the vapor will be forced away from the crankcase and end up in the suction line This refrigerant may condense in the suction line and cause slugging in the compressor s cylinders on start up Slugging is liquid refrigerant or liquid oil act
8. to the compressor s crankcase Oil separators are located close to the compressor in the discharge line Even though most oil separators are designed to be mounted vertically there are some horizontal models available on the market Oil separators are essential on low and ultra low temperature refrigeration systems and on large air con ditioning systems up to 150 tons Most compressor manufacturers require oil separators on all two stage compressors Oil separators can also act as discharge mufflers to quiet compressor pulsation and vibration noises Unusual conditions occur at times to compressors and rapid removal of oil from the compressor s crankcase happens A lot of times these occurrences happen beyond the control of both the designer and installer The velocity of the refriger ant flowing through the system should return oil to the compressor s crankcase Even though proper refrigerant system piping designs maintain enough refriger ant velocity to ensure good oil return sometimes this added pressure drop which assists in getting the right refrigerant velocity for oil return hampers the system s efficiencies A lot of times a higher than normal pressure drop is intentionally designed into a system for better oil return This will cause higher compression ratios and lower volumetric efficiencies leading to lower capacities A helical oil separator Courtesy Ferris State University Detrimental Effects of Oil in a System O
9. which will open when energized and vent the trapped refrigerant to the common suction header through a capillary tube restriction Both the bleed hole in the piston or the capillary tube ensure that the refrigerant experiences a restriction and is mostly vaporized before reaching the common suction header which is under low side common suction pressure A check valve is located at the summer condenser s outlet to prevent any refrigerant from entering it while it is idle and under a low pressure condition While not needed for backflow prevention a check valve is also located at the outlet of the summer winter condenser simply to make the pressure drops egual in both halves of the condenser when both are being used simultane ously in summertime operations www a as com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Helical Oil Separators ecause refrigerants and refrigeration oils are miscible in one anoth er there will always be some oil that leaves the compressor with the refrigerant being circulated Also any time flooding or migration occurs crankcase oil is sure to be diluted with refrigerant This will cause oil foaming at start ups Crankcase pressures will build often forcing oil and refrigerant around the rings of the compressor s cylinders to be pumped into the discharge line Oil separators remove oil from the compressor s discharge gas temporarily store the oil and then return it
10. a cloth barrier and monitor for 10 minutes as above 5 If the results are positive uncover the equipment and begin spray coat ing with a microfoam solution If the results are negative continue to the suc tion liquid line leak test that follows Suction Liquid Line Leak Test The longer the tubing runs are between the evaporator and condensing unit the greater is the odds for defects Count on all possibilities whether it be a typical sight glass drier connection leak to a poor solder joint hidden under pipe insulation Figure 3 In testing for leaks cover the condensing unit with a cloth tarp or bed sheet to serve as a barrier against any outside air movement and to trap refrigerant gas Photo courtesy of Refrigeration Technologies Anaheim Calif The suction line can be screened by calibrating an electronic leak detector to its highest sensitivity Tuck the probe underneath the pipe insulation Monitor for 10 minute intervals while the system is at rest and fully pressurized to equal ization It may be necessary to insert the probe at several downstream points If a leak is sensed strip off insulation and apply a bubble foam promoter to all surfaces If no leak was positively screened test the liquid line www 00 com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Advanced Leak Detection he last chapter introduced the topic of leak detection and provided de tails on basic det
11. a solid scaling the equipment This concentration OLPHIN a WATERCARE ae Figure 1 Signal generator and water treatment module installed in a working cooling tower Courtesy of Clearwater Systems Corp www z com Y fink and attraction of particles eventually becomes hard eguipment damaging scale Now a proprietary and patented technology has been developed by an engineering and research team This chemical free technology eliminates scale inhibits bacterial growth and inhibits corrosion in water purifi cation Figure 1 How it Works When the cooling tower water holding these small suspended particles passes through a water treatment module and is activated by a high freguency electrical pulse field the natural electrical static charge on the particle s surface is removed In removing this surface charge on the suspended particles they are now the preferred site for precipi tation of minerals to occur instead of the equipment surfaces The suspended particles now act as seeds for precipitation of dissolved minerals Thus the hard scale is prevented from forming on the equipment s surfaces and instead bonds to the tiny suspended par ticles in the water The minerals in the water now adhere to and coat the suspended particles As more and more minerals bond to the suspend ed particles they become heavier and can no longer suspend themselves in the water stream They eventu ally make their way to the
12. actually part of the liquid line Courtesy of Sporlan Division Parker Hannifin Corp www eae com fin ke Book HVACR Service and Troubleshooting With The Professor very light load on the compressor caus ing the amp draw to be low Short cycle on the low pressure control LPC The compressor may short cycle on the LPC depending on how severe the restriction in the TXV is The low suction pressures may cycle the compressor off prematurely After a short period of time the evaporator pressure will slowly rise from the small amounts of refrigerant in it and the heat load on it This will cycle the compres sor back on This short cycling may keep occurring until the compressor over heats Short cycling is hard on controls Capacitors and motor windings the NEWS ke Book HVACR Service and Troubleshooting With The Professor Basic Leak Detection Methods very environmentally conscious service technician should spend time learning how to check for refrigerant leaks in refrigeration and or air conditioning systems Ozone depletion global warm ing and the increasing price of refrigerants are forcing techni cians to become better and more thorough leak detectors This chapter will cover some basic methods of leak detection in refrigeration and air conditioning systems The next chapter will look at some of the more advanced methods Leak Detection Methods All sealed systems leak The leak could be 1 pound per second
13. age from its internal battery to detect high resistance problems like deteriorated winding insula e Book HVACR Service and Troubleshooting With The Professor tion moisture or other system contamination Listed below are some other important tips service technicians should know about the use of a megohmmeter e Never use a megger if the motor windings are under a vacuum e Meggers can be used for other electrical devices other than electric motors e Always consult with the meter manufacturer or user s manual for de tailed instructions on megging other electrical devices like coils e Meggers are often used in preventive maintenance programs especially before a contractor signs a preventive maintenance contract to determine condition of the electrical devices e Any megger with a higher voltage output than 500 volts DC should be used by an experienced technician A high voltage for too long of a time may further weaken or fail motor windings and the winding insulation could be damaged by the testing procedure www s com Y fink the N EWS e Book HVACR Service and Troubleshooting With The Professor Bad Compressor Valves any servicemen experience service calls where the com pressor has both a low head pressure and a high suction pressure Often the refrigeration eguipment is still running but the product temperature is suffering about 7 to 10 F These calls are tough to handle because the compressor is s
14. ake ma chine troubleshooting The previous chapter examined trou bleshooting low and high water levels This chapter will ex amine problems associated with water impurities as well as mechanical problems When water is frozen in an evaporator flooded with water minerals in the water will often build up on the walls of the evaporator This mineral buildup will cause added resistance for the ice cutting auger Mineral buildup scale is a porous material and is a good insulator to heat transfer The refrigerant will now see less heat load from the water in the cylinder and the evaporator pressure will drop A drop in evaporator pressure will cause a colder evapo rator and harder ice The cutting auger s flights now have to cut harder ice along with minerals that have built up on the evaporator surface The result is a loud crunching or squealing noise coming from the evaporator compart ment This added resistance of cutting ice and mineral buildup will also add extra load on the gear motor A higher amp draw will be the result Drive Train Gears Shafts When the ice cutting auger is stressed so is the gear motor and drive train The ice cutting auger drive train with gears and the gear motor are all con nected Figure 1 When the gear motor is stressed from cutting hard ice and minerals the extra torque generated from the motor will cause excessive heat This may cause the gear motor s overload to open and shut the unit down until a
15. and the mixture of refrigerant and oil foam can now be forced through compres sor passages and around piston rings and be pumped by the compressor Not only does this situation cause loss of oil from the crankcase to the system but it can also cause a mild form of slugging in the compressor s cyl inders High compressor current draw which will lead to motor overheating usually follows Also broken or warped valves can occur as a result of over heating and or slugging Solution The only sure solution in avoiding migration is to get rid of all the refriger ant in the evaporator suction line and crankcase before the off cycle An au tomatic pump down system can accomplish this A thermostat controlling box temperature is wired in series with a liquid line solenoid When the box tem www 000 com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Compressor Motor Oil safety oro contactor switch protector i High pressure Low pressure switch switc NC Thermostat Defrost zt timer Liquid line solenoid Defrost heater Figure 1 Schematic diagram of an automatic pump down system Figure from Troubleshooting and Servicing Modern Air Conditioning and Refrigeration Systems by John Tomczyk perature is satisfied the thermostat contacts will open This will de energize the liquid line solenoid and a pump down cycle will be initiated Soon all the liquid and
16. and how they affect other components of the ice flake machine Low Water Levels If a float mechanism in the water reservoir is adjusted wrong and the water level is low in the reservoir it will also be low in the freezing cylinder Figure 1 A cutting edge or flight is shown to the right in this photo of an auger Courtesy of Ferris State University because of water seeking its own level Since water is the refrigerating load for an ice flake machine low water level in the freezing cylinder means low load on the evaporator This condition will cause lower than usual evaporator pressures thus lower evaporator temperatures These low evaporator temperatures will produce harder and colder ice for the auger to cut This will put an extra load on the auger gears and gear motor Often the gear motor will trip on its overload and sometimes has to be manually reset Water reservoirs should have a line indicating the correct water level for that particular machine www EA com Y fink WATER WATER CONTROL INLET VALVE EVAPORATOR FLOAT a SWITCH W WATER LEVEL EXPANSION M VALVE i fe al if n Ie TIS i IRS a RESERVOIR x OVERFLOW DRAIN J OUTLET hu he A i m bj Ann EXCHANGE 7 TI A GEAR MOTOR p DRAIN PAN FLUSH WATER VALVE Figure 2 This schematic shows the relationship of the water level with the freezing cylinder in a flake ice machine Courtesy of Hoshizaki A
17. apping the procedures already mentioned At least two and usually three procedures should be merged into one procedure This type of testing requires a high order of skills and observation techniques Each sus pected component must be isolated and tested in the following manner www E AN com Y fink the N EWS Such superfine leak testing is beyond the normal operations of the service technician Microleaks are considered an acceptable amount of leakage in our industry at this point in time 1 A valve or fitting is subjected to high pressure 2 Spray coat the valve or fitting 3 Tap the component repeatedly with a rubber mallet to induce vibration If there s no leakage then go to step 4 e Book HVACR Service and Troubleshooting With The Professor 4 Gently add heat to the component If no leakage continue on to another component Cumulative Microleaks The sixth and final classification of leaks discussed over these past two chapters was a cumulative microleak that is measured using a helium mass spectrometer Such superfine leak testing is beyond the normal operations of the service technician Microleaks are considered an acceptable amount of leakage in our industry at this point in time Note The technical information and photographs contained in this chapter and the previous chapter on leak detection were used with the permission of Refrigeration Technologies Anaheim Calif www sae com Y fink
18. bed in the evaporator section there will be hardly any heat to be rejected into the condenser section of the system This will keep condensing head pressures down Talk Is Good Many technicians will try to add refrigerant when they experience low suc tion and low head pressures simultaneously This is not always the answer It is true an undercharge of refrigerant will cause low head and low suction pres sures but that is not the only thing that will cause both pressures to be low An undercharge will have low subcooling readings on the high side where a dirty air filter for the evaporator will not produce low subcooling readings In this case something as simple as a dirty air filter was the culprit in freezing the coil and causing low head and suction pressures In this case the low airflow was the major clue to the problem and it wouldn t have been noticed if the technician did not converse with the homeowner before trouble shooting Hopefully the service technician would have eventually taken a sub cooling reading if the low airflow problem was not noticed www 0 com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Condenser Splitting his chapter focuses on the concept of condenser splitting But first here s a quick review of condenser flooding before covering condenser splitting to help the reader better under stand both of these concepts and their particular advantages and disa
19. bubbles stand for at least 10 15 minutes if small leaks are suspected Another advantage of bubble testing is that bubbles can be used with ni trogen or refrigerants pressurizing the system Small significant leaks of less than a couple ounces per year can often be found with special formulated mi crofoam solutions If the evaporator section tests negative for leaks continue on to leak testing the condensing unit www B com Y fink the NEWS eBook HVACR Service and Troubleshooting With The Professor Testing for Condensing Section Leaks To test for condensing section leaks 1 Calibrate an electronic leak detector to its highest sensitivity and place the probe at the base of the unit usually under the compressor The unit should be fully pressurized 2 Cover the condensing unit with a cloth tarp or bed sheet to serve as a bar rier against any outside air movement and to trap refrigerant gas Figure 3 Do not use a plastic material because some plastics may set off some electronic leak detectors and give a false reading 3 Monitor for leakage for 10 minutes or until a leak is sensed Recali brate and test again Two consecutive positive tests confirm condensing sec tion leakage Two consecutive negative tests rule out a detectable leak 4 Use the electronic leak detector to check for leaks on the bellows of the pressure controls Remove the control box cover and place the probe within the housing Cover the control tightly with
20. c cur while the unit is in operation are the rarest of all leaks They are cracks that open and close from physical shaking However studies have shown that certain components and piping on refrigeration units will develop vibration leaks An electronic leak detector or a microfoam solution can be used while the unit is running Again drafts have to be minimized when the unit is run ning for use of an electronic detector If an electronic detector is used first a blanket or sheet should be used to help collect escaping gases and mini mize air currents If a microfoam solution is used place the unit in operation and spray coat the following areas with the solution Look for large bubbles or foam cocoons formations Large bubbles will form on larger leaks Figure 4 and foam co coons will form on small leaks Below are areas to spray coat e All compressor bolts and gasket edges e Suction line connection at compressor e Suction line connection at evaporator e Discharge line connection at compressor e Discharge line connection at condenser e Vibration eliminators e Any joint or fitting on unsupported pipe runs e Expansion and solenoid valves Figure 4 Large bubbles form on larger leaks Courtesy of Refrigeration Technologies Anaheim Calif e Capillary tube connections and Sight glass Combination Dependent Leaks Dealing with combination dependent leaks the fifth classification of leaks involves overl
21. ces ADL BUGAZ This book will give you the knowledge you need to safely install residential forced air furnaces properly Learn important safety tips and how to install a thermostat power wiring piping ductwork and vents Information on installing a split system is included A chapter also covers The HVACR industry requires more specialized skills and information than any other trade and this new book meets that demand head on With more than 500 pages of extensive information on such important topics as refrigeration systems piping ductwork motors compressors fans pumps and INDOOR ENVIRONMENT TECHNICIAN S LIBRARY Ai i i more this answer book is one of the customer relations Review questions most complete HVACR professional at the end of each chapter make this references available an excellent class text book Go to www achrnews com products category 2166 product 566 Go to www achrnews com products category 2166 product 570 for more information and to order for more information and to order the N EWS OVER 100 PRODUCTS FOR THE HVACR Industry
22. ces that there is a floodback problem during the running cycle Floodback can ruin a compressor by diluting the compressor s oil with liquid refrigerant This has a tendency to ruin the lubricity of the oil and score bear ing surfaces in the compressor Floodback also causes oil foaming which can Cause oil to be pumped out the discharge valve and into the system Discharge valve damage can also occur from the oil foam refrigerant rich mixture Finding a Cause The technician then checks the airflow problem and agrees with the home owners that there is a reduced airflow problem The technician then takes a cur www ian com Y fink the N EWS rent reading of the fan motor and finds it to be 4 2 amps This is far from the nameplate current of 8 amps This tells the technician that the fan motor is only partially loaded and is not moving the proper amount of air it is designed to move The technician then decides to check the air filter located in the return air cabinet before the evaporator or A coil He notices that it is completely filled with dust and lint However even with the air filter pulled there still is a re stricted airflow problem and the fan motor continues to pull low current He then decides to have a look at the A coil itself He shuts off power to the unit and removes the plenum He finds that the A coil is completely covered with a blanket of ice and frost The technician then melts the iced coil with a large watta
23. chines employ an auger rotating within an insulated freezing cylinder or evaporator The auger which is driven and geared down by a gear motor and gear box to about 8 16 rpm has cutting edges or flights The flights shave ice from the walls of the freezing cylinder evapora tor which is flooded with water and has refrigerant lines wrapped around its outer circumference Figure 1 The refrigerant lines have vaporizing refrig erant in them which will freeze the water that is in close proximity or contact to the inside of the freezing cylinder A water reservoir supplies the right height or level of water to the freezing cyl inder Because water will seek its own level the water level or height in the water reservoir will also be the level in the freezing cylinder Figure 2 on the next page Water level in the reservoir is usually controlled by a single float mechanism or a dual float mechanism which controls an electric solenoid valve to bring water to the reservoir The water logged shaved ice is then carried through the water to the top or head of the freezing cylinder where it is squeezed extruded shaped cut and eventually falls to an insulated ice storage bin for use Figure 3 on the next page It is of utmost importance that the water level in the reservoir and freezing cylinder are at the proper levels for the ice flake machine to operate effectively What follows are some scenarios for improper water levels in the freezing cyl inder
24. ck valve in the partition between the crankcase and the motor barrel will pre vent any liquid refrigerant from entering the crankcase High current draws will be noticed here from dense refrigerant vapors entering the compressor s cylinder Most hermetic compressor s suction lines end at the shell of the compres sor If liquid refrigerant is entering the compressor liquid will fall directly into the crankcase oil and eventually be flashed As mentioned earlier this is referred to as flooding This causes oil foaming and excessively high crankcase pressures Refrigerant and oil droplets will soon reach the compressor s cylin der and slugging will soon occur Slugging in hermetic compressors can also occur from a migration prob lem As mentioned before foaming oil and refrigerant in the crankcase due to migration will generate excessive crankcase pressures when the on cycle occurs These oil and refrigerant droplets can now get past piston rings and other small openings and enter the compressor s cylinder The end result is slugging of refrigerant and oil Slugging can damage reed valves piston rods bearings and many more mechanical parts Conclusion Clarification and understanding of these two technical terms can help technicians troubleshoot and remedy even the most complex compressor breakdowns www 00 com Y fink CHECK OUT THE NEWS HVACR INDUSTRY STORE J TE i a st ig Installing Residential Forced Air Furna
25. cooling tower s basin as a harmless fluffy powder or tiny coated particle This powder or coated particle can easily be removed from the cooling tower s basin by manual means filtration or centrifugal separation The quantity of powder is typically about 15 percent of nor mal blow in dirt in a cooling tower Particle Separator Particles can be removed from the bottom of the cooling tower s basin using a centrifugal separator Figure 2 Water from the basin is pumped to a centrifu gal separator where it enters the separator tangentially This gives the water the proper inlet veloc ity and causes a constant change of direction to generate an initial vortexing action Internal tangential slots lo cated on the inner separation bar rel causes the water to accelerate further and magnify the vortex Inlet Liquid solids enter unit tangentially which sets up a circular flow Vortube reduces pressure in the collection chamber to enhance separation Solids free liquid is drawn to the separator s vortex and up through the separator s outlet Purge Solids are either periodically purged or continuously bled from the separator as necessary www achrnews com Y fink Liquids solids are drawn through the patented Swirlex tangential slots and accelerated into the separation chamber Centrifugal action directs particles heavier than the liquid to perimeter of separation chamber Solids gently drop along p
26. d pressures Normal Evaporator Superheats The TXV will try to maintain super heat even at an excessive overcharge As mentioned above the TXV may overfeed slightly during its opening strokes but then should catch up to itself if still in its operating pressure ranges High Compression Ratios The condenser flooded with liquid during the overcharge will run high condensing pressures This causes high compression ratios and causes low volumetric efficiencies causing low refrigerant flow rates Overcharged Capillary Tube Systems If we are dealing with a capillary tube metering device the same symp toms occur with exception to the evaporator superheat Remember capillary tube systems are critically charged to prevent liquid floodback of refrigerant to the compressor during low evaporator loads The higher head pressures of an overcharged system incorporating a capillary tube as a metering device will have a tendency to overfeed the evaporator thus decreasing the superheat If the capillary tube system is severely overcharged liquid can enter the suction line and get to the suction valves or crankcase This will cause com pressor damage and eventually failure Again it is the system check sheet that will tell the service technician whether a system is overcharged or not Service technicians must install pres sure gauges and thermistors or some other sort of temperature sensing devic es in order to systematically troubleshoot a refrigeration
27. dvantages Condenser Flooding A pressure actuated holdback valve is installed at the condenser outlet This valve is often referred to as an ORI Open on Rise of Inlet valve The valve will throttle shut when the condenser pressure reaches a preset mini mum pressure in a cold ambient condition Figure 1 This throttling action will back up liquid refrigerant in the bottom of the condenser causing a flood ed condition The condenser now has a smaller internal volume which is what is needed for a colder ambient condition The condenser pressure will now rise giving sufficient liquid line pressures to feed the expansion valve Larger receivers are needed for these systems to hold the extra refrigerant for con denser flooding in the summer months While the condenser is being flooded with liquid refrigerant a CRO Close on Rise of Outlet valve located between the compressor s discharge line and the receiver inlet will bypass hot compressor discharge gas to the receiver inlet when it senses a preset pressure difference between the discharge line and the receiver Figure 1 The T symbol means the valve comes with a built in pressure tap for ease in taking a pressure reading for service purposes and for setting the valve The pressure difference is created from the reduced flow of refrigerant to the receiver because of the throttling action of the ORI valve The bypassed hot gas External Equalizer Solenoid Valve Catch A
28. e ful that the leak detector probe does not come into contact with any water 6 Sniff with the electronic detector for a minimum of 10 minutes or until a leak is sensed Recalibrate the device and test again Two consecutive pos itive tests confirm an evaporator leak Two consecutive negative tests rules out an evaporator section leak Remember refrigerant gas is heavier than air Gravity will cause the gas to flow to the lowest point If the evaporator section tests positive the technician should expose the coil and spray coat all surfaces with a specially formulated bubble foam promoter Bubble microfoam solutions have been very successful in leak detection because of their price and effectiveness Leaks can be easily pinpointed with these solutions Often a mild soap and water solution is used for bubble checking Re search has shown that soap and water does not have the same properties as do the micro foam solutions that contain coagulants and wet adhesives Household deter gents often contain chlorides and will pit and corrode brass and iron The specially formulated and patented bubble solutions have entered the market with remarkable results These new solutions will form a foam co coon when in contact with a leak All that is required is for the solution to be applied over the suspected leak area When a leak is found bubbles or foam will tell the technician of its location The technician must be patient and let the
29. e condenser is being starved of refriger ant it can operate at a lower temperature and pressure This is because it does not need a large temperature difference between the ambient and the condensing temperature to reject the small amount of heat it is getting from the evaporator suction line and compressor This temperature difference is referred to as the condenser split If there were large amounts of heat to reject in the condenser the condenser would accumulate heat until the con denser split was high enough to reject this large amount of heat High heat loads on the condenser mean large condenser splits Low heat loads on the condenser mean low condenser splits Normal to a bit high condenser subcooling Most of the refrigerant will be in the receiver with some in the condenser The condenser subcooling will be normal to a bit high because of this The refrigerant flow rate will be low through the system from the restriction This will cause what refrigerant that is in the condenser to remain there longer and subcool more Note that an undercharge of refrigerant will cause low subcooling Low evaporator pressures Since the evaporator is starved of refriger ant the compressor will be starving also and will pull itself into a low pressure situation It is the amount and rate of refrigerant vaporizing in the evapora tor that keeps the pressure up A small amount of refrigerant vaporizing will cause a lower pressure e Book HVACR Service
30. e will also be higher than nor mal The resulting symptom will be a lower head pressure with a higher suction pressure The symptoms for worn rings on a compres sor are very similar to leaky valves Figure 2 Worn compressor rings sor crankcase through a small return line The pressure difference between the high and low sides of the refrigeration system is the driving force for the oil to travel from the oil separator to the compres sor s crankcase The oil separator is in the high side of the system and the compressor crank case in the low side The float operated oil return needle valve is located high enough in the oil sump to allow clean oil to automatically return to the compres sor s crankcase Only a small amount of oil is needed to actuate the float mechanism which ensures that only a small amount of oil is ever absent from the compressor crank case at any given time When the oil lev el in the sump of the oil separator drops to a certain level the float forces the needle valve closed When the ball and float mechanism on an oil separator goes bad it may bypass hot discharge gas di rectly into the compressor s crankcase The needle valve may also get stuck par Leaky Oil Separator tially open from grit in the oil This will cause high pressure to go directly When the oil level in the oil separator becomes high enough to raise a into the compressor s crankcase causing high low side pressures and low f
31. ection methods This chapter will look at more ad vanced methods You may recall that the previous chapter outlined various classes of leaks with standing leaks as the most common How to deal with such leaks was covered in that chapter as the first classification of leaks Pressure Dependent Leaks The second classification was the pressure de pendent leaks which can only be detected as the sys tem pressure increases So we will begin with a dis cussion of how to test for pressure dependent leaks First you need to pressurize the low side to 150 psig and the high side to 450 psig using dry nitrogen The equipment rating plate usually states the maximum pressure permissible Also always make sure that valving and other components can take these pressures whether they are original equipment or not If the high side and low side cannot be split by ways of isolation valves pressurize the entire system to about 350 psig if permissible Warning Never use pure oxygen or air to raise the pressure in a refrigera tion system Pure air contains about 20 percent oxygen The pure oxygen and or the oxygen in the air can combine with refrigerant oil and cause an explosive Figure 1 In using a micro foam solution for leak testing allow up to 15 minutes reaction time Photo courtesy of Refrigeration Technologies Anaheim Calif mixture Even some refrigerants when mixed with air or oxygen can become explosive under pressure Pure oxygen a
32. ed value Compressor discharge temperature 250 F Condenser outlet temperature O Evaporator outlet temperature KONE Compressor inlet temperature 251P Ambient temperature ZOE Box temperature Sh Compressor volts 2300 Compressor amps High Low side evaporator pressure 6 2 sie COF High side condensing pressure 185 5 sig G25 F Item to be calculated Calculated value Condenser split 515 e Condenser subcooling sae Evaporator superheat 10 F Compressor superheat 25 F larities of symptoms in both scenarios of an overcharge of refrigerant and restricted airflow over the condenser System Containing Air Another similar scenario would be a refrigeration system containing air as in Table 3 Air is a noncondensable and will get trapped in the top of the condenser This will cause high head pressures and high condensing temper www ie com Y fink the NEWS This phenomenon happens because the temperature difference between the liquid at the condenser s bottom and the surrounding ambient is the driving potential for heat transfer to take place As more and more air is restricted from flowing through the condenser the amount of condenser subcooling will increase atures because of reduced condenser volume to desuperheat condense and subcool Thus the liquid at the condenser s bottom will be hotter than nor mal and will lose heat faster to the ambient This will result in an increase in condenser subcooling
33. endent on the careful observation made by the testing technician Fortunately all refrigeration systems inter nally circulate compressor oil with the refrigerant Oil will blow off with the leaking refrigerant gas and oil mark the general area of leakage Oil spots appear wet and have a fine coating of dust Figure 1 The technician must determine that the area wetness is oil and not condensate This can be ac complished by rubbing the area with your fingers and feel for oil slickness However what is the reliability of oil spotting Oil spotting is the technician s SS SS S gt K p e gt Figure 1 In leaking systems oil spots can appear wet and have a fine coating of dust Photo courtesy of Refrigeration Technologies Anaheim Calif first quick check but is not always reliable for the following reasons e Qil is always present at Schrader valves and access ports due to the dis charging of refrigerant hoses on the manifold and gauge set Figure 2 next page Often these parts are falsely blamed as the main point of leakage e Qil blotches can originate from motors pumps and other sources e Qil residue may be the result of a previous leak e Oil is not always present at every leak site It may take months even years of unit operation to cause enough oil blow off to accumulate on the outer side e Oil may not be present with micro leaks e Oil may not reach certain leak positions e Oil may not be prese
34. enser subcooling amounts to a level where the head pressure may elevate This is caused from a lack of internal volume in the condenser to hold the added refrigerant Even the receiver may overfill if too much refrigerant is added Table 1 on the next page shows a system checklist for a system with a re stricted metering device Symptoms can include e Somewhat high discharge temperature e Low condensing head pressure e Low condenser split e Normal to a bit high condenser subcooling e Low evaporator suction pressure e High superheats e Low amp draw and e Short cycle on low pressure control LPC Symptoms High discharge temperature Somewhat high discharge temperatures are caused by the higher superheats from the evaporator being starved of refrigerant The compressor is now seeing a lot of sensible heat coming from the evaporator and suction line along with its heat of compression and mo www ae ae com Y fink the N EWS tor heat The compressor will probably overheat from the lack of refrigerant cooling if it is a refrigerant cooled compressor Low condensing head pressures Since the evaporator and compres sor are being starved of refrigerant so will the condenser because these com ponents are in series with one another There will be little heat to eject to the ambient surrounding the condenser This allows the condenser to operate at a lower temperature and pressure Low condenser splits Since th
35. erheats may be the result However the superheats may be normal if the valve problem is not real severe High evaporator suction pressure Refrigerant vapor will be drawn from the suction line into the compressor s cylinder during the downstroke of the compressor However during the upstroke this same refrigerant may sneak back into the suction line because the suction valve is not seating prop erly The results are high suction pressures Low amp draw Low amp draw is caused from the reduced refrigerant flow rate through the compressor During the compression stroke some of the re www eh sie com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor frigerant will leak through the suction valve and back into the suction line reducing the refrigerant flow During the suction stroke some of the refrigerant will sneak through the discharge valve because it is not seat ing properly and get back into the com pressor s cylinder In both situations there is a reduced refrigerant flow rate causing the amp draw to be lowered The low head pressure that the compressor has to pump against will also reduce the amp draw Worn Compressor Rings When the compressor rings are worn high side discharge gases will leak through them during the compression stroke giving the system a lower head pressure Figure 2 Because discharge gases have leaked through the rings and into the crankcase the suction pressur
36. erimeter and into the separator s quiescent calm collection chamber Vortex flow draws fluid and pressure from the solids collection chamber via the Vortube for enhanced performance Figure 2 left The removal of particles at the bottom of the cooling tower s basin can be accomplished using a centrifugal separator Courtesy of Lakos Separators and Filtration Solutions strength Particles in the water are now separated through centrifugal action caused by the vortex The particles spiral downward along the perimeter of the inner separa tion barrel and are deposited ina collection chamber below the vor tex deflector plate where they can be automatically purged Free of separable particles the water spirals up the center vortex in the separation barrel and up ward to the outlet A vortex driv en pressure relief line draws fluid from the separator s solids col lection chamber and returns it to the center of the separation bar rel at the vortex deflector plate This allows even finer solids to be drawn into the solids collection chamber that would otherwise be re entrained in the vortex the NEWS ke Book HVACR Service and Troubleshooting With The Professor Bacterial Control There are two methods of controlling bacteria or microbial population in cooling tower systems encapsulation and electroporation Normally bacteria form a biofilm or slime layer on eguipment surfaces The slimy bacterial secretion for
37. f the refrigeration to in crease causing higher pressures in the evaporator One must slowly control the amount of warm water introduced to avoid temperature shock to the evaporator The rupture disc on the evaporator may open if the pressures are raised too high There are special fittings available from the chiller manufacturer to equalize pressure inside and outside of the rupture disc to prevent rupture Please consult with the chiller manufacturer before attempting to service or leak check any chiller An electronic leak detector may be used while the system is running How ever running a system usually causes a lot of fast air currents from fans and motors that may interfere with electronic detection It helps to cover the unit with a blanket or sheet to try to collect escaping refrigerant gases The leak ing refrigerant will be easier to pick up with an electronic detector if it can collect somewhere instead of being dissipated by air currents 2 Spray coat all metal connections with a microfoam solution Figure 3 www es com w fin the NEWS ke Book HVACR Service and Troubleshooting With The Professor one at a time and observe for leakage Rewet any extremely hot surfaces with water to keep the fluid from evaporating too quickly 3 When testing evaporator components you may induce heat by placing the unit into defrost Vibration Dependent Leaks The fourth classification of leaks is vibration dependent Leaks that only o
38. filter drier changes 20 moisture and or Change oil if acid is present contamination 20 0 Severe contamination Check entire system and make 15 corrections Consider an oversized filter drier refrigerant and oil change and re evacuation System burnout and clean up procedures required Figure 1 Also read the instructions that come with the meter to determine what time interval to energize the megger when checking winding or coils If pos sible it is a good idea to run the motor for at least one hour disconnect power disconnect all electrical leads and then quickly connect the megger to the motor This will give a more meaningful comparison between readings for the same compressor on different days because of the approximate same winding temperatures Good motor windingreadingsshouldhavearesistancevalueofaminimumof100 megohms relative to ground Infact good motor winding resistance should be be tween 100 megohms and infinity www sae aie com Y fink the N EWS Regular preventative maintenance checks can be made with a megohmmeter and can signal early motor winding breakdown from a contaminated system when accurate records are kept Figure 1 lists megohm readings with varying degrees of contamination and motor winding breakdown Because of the very high resistance of the motor winding insulation a regular ohmmeter cannot be used in place of the meg ger A regular ohmmeter does not generate enough volt
39. forced out of the cylinder and into the discharge line during the upstroke of the compressor On the downstroke this same refrigerant that is now in the discharge line and com pressed will be drawn back into the cylinder because the discharge valve is not seating properly This short cycling of refrigerant will cause heating of the discharge gases over and over again causing higher than normal discharge temperatures However if the valve problem has progressed to where there is hardly any refrigerant flow rate through the system there will be a lower discharge temperature from the low flow rate Low condensing head pressures Because some of the discharge gases are being short cycled in and out of the compressor s cylinder there will be a low refrigerant flow rate to the condenser This will make for a reduced heat load on the condenser thus reduced condensing head pres sures and temperatures Normal to high condenser subcooling There will be a reduced refrig erant flow through the condenser thus through the entire system because components are in series Most of the refrigerant will be in the condenser and receiver This may give the condenser a bit higher subcooling Figure 1 Overheating and discoloring of a discharge valve All photos courtesy Ferris State University Normal to high superheats Because of the reduced refrigerant flow through the system the TXV may not be getting the refrigerant flow rate it needs High sup
40. g A float activated oil return valve allows the captured oil to return to the compressor s crankcase or oil reservoir When the level of oil gets high enough to raise a float an oil re turn needle is opened and the oil is returned to the compressor s crankcase through a small return line connected to the compressor s crankcase The pressure difference between the high and low sides of the refrigera tion or air conditioning system is the driving force for the oil to travel from the oil separator to the crankcase The oil separator is in the high side of the system and the compressor s crankcase is in the low side This float operated oil return needle valve is located high enough in the oil sump to allow clean oil to be automatically returned to the compressor s crankcase Only a small amount of oil is needed to actuate the float mechanism This ensures only a small amount of oil is ever absent from the compressor s crank case at any given time When the oil level in the sump of the oil separator drops to a certain level the float will force the needle valve closed On larger parallel compressor systems the oil separator gives the oil to an oil reservoir for temporary storage until a compressor calls for it The oil reservoir is usually kept at a pressure at about 20 psi above the common suction header pressure by a special pressure regulating valve Many times there may be a combination oil separator reservoir In this case the oil i
41. ge Learning He is author of the book Trouble shooting and Servicing Modern Air Conditioning and Refrigeration Systems published by ESCO Press He is also author of an EPA approved Technician Certification Program Manual and a Universal R 410A Safety and Retrofitting Train a ing Manual He also is a monthly columnist for Air Conditioning Heating and Refrigeration News magazine Tomczyk has 28 years of teaching ex perience at Ferris State University in Big Rapids Mich along with many years of HVACR service experience To order the book Refrigeration and Air Conditioning Technology call 800 648 7450 Tomczyk can be reached by email at tomczykjohne gmail com 20 0 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000G00000000000c0n0000000 Published by The Air Conditioning Heating and Refrigeration News September 2012 Copyright 2012 BNP Media All Rights Reserved No part of this book may be reproduced or used in any manner except as permitted by the U S Copy right Act without the express written permission of the publisher Every effort has been made to ensure the accuracy of the information presented in this book However BNP Media does not guarantee its accuracy Any error brought to the attention of the publisher will be corrected in a future edition For ordering infor mation go to www achrnews com products www com Y fink the NEWS ke Book HVACR Service and Troubleshoot
42. ge blowdryer After putting the plenum back on the unit and installing a new air filter the technician starts the air conditioner The proper airflow has been established and the suction pressure is normal at 70 psig The fan motor is now drawing normal current of about 7 amps The technician then explains to the homeowner that a dirty air filter has caused a restricted airflow to the A coil He then explains the importance of keeping the air filter clean This restriction in the airflow has caused a low suction pressure because of a reduced heat load entering the evaporator coil This caused a slower vaporization rate of refrigerant in the evaporator The low suction pressure made the refrigerant flowing through the evaporator below freezing 26 This finally froze the evaporator coil solid with ice The restricted airflow also unloaded the fan motor causing it to draw low current Once the evaporator coil froze solid the refrigerant saw very little heat e Book HVACR Service and Troubleshooting With The Professor and humidity load This caused a low vaporization rate and some of the liguid refrigerant R 22 trickled down the suction line to the compressor s crank case causing floodback This is why there were only 2 of compressor super heat and the crankcase area was cold to the touch The low heat and humidity load on the evaporator also caused the head pressure to be low This happened because if there was very low heat be ing absor
43. gh compressor current draw This may overheat and even trip the compressor Broken valves can also occur from this phenomenon A telltale sign that a compressor s crankcase is being flooded with refrigerant will be a cold frosted or sweaty crankcase A foaming compressor s oil sight glass with a low oil level are also signs of flooding Higher than normal current draws will also be present Slugging Slugging is liquid refrigerant or liquid refrigerant and oil entering the compressor s cylinder during an on cycle Causes could be No compressor superheat e Migration off cycle e Bad TXV e TXV hunting e Low load e End of cycle lowest load e Evaporator fan out e Iced evaporator coil e Defrost timer or heater out e Dirty evaporator e Capillary tube overfeeding and e Overcharge Air cooled semi hermetic compressors are more prone to slugging liguid than refrigerant cooled semi hermetic compressors This is because refrigerant is of ten drawn directly into an air cooled semi hermetic compressor s cylinder with out passing through the motor barrel Slugging can result in broken valves broken head gaskets broken connecting rods and other major compressor damage Refrigerant cooled semi hermetic compressors will often draw liquid from the suction line through hot motor windings in the motor barrel which will assist in vaporizing any liquid Even if liquid refrigerant gets past the motor windings the che
44. gurations may apply when using capillary tubes as metering devices different system symptoms may occur The intent of this chapter is to explore how a par tially restricted TXV will affect system performance and efficiency and what symptoms will occur Listed below are ways the metering device TXV can become restricted e Plugged inlet screen Foreign material in orifice e Oil logged from refrigerant flooding the compressor e Adjusted too far closed e Wax buildup in valve from wrong oil in system e Sludge from the byproducts of a compressor burnout e Partial TXV orifice freeze up from excessive moisture in the system and e Manufacturer s defect in the valve A system with a restricted metering device has the very same symp toms as a system with a liquid line restriction that occurred after the re ceiver This is because the TXV is actually part of the liquid line A TXV being restricted will cause the evaporator compressor and condenser to be starved of refrigerant This will cause low suction pressures high super heats low amp draws and low head pressures Also the symptoms of a restricted TXV system are very similar to a sys tem with a refrigerant undercharge However the undercharged system will have low condenser subcooling levels Service technicians often confuse an undercharged system with a restricted metering device Adding refrigerant to a system with a restricted metering device will only raise the cond
45. he condenser s bottom will be hotter because of the elevated condensing temperatures This creates a greater temperature difference between the liquid at the condenser s bottom and the ambient surrounding air designed to cool the condenser and its liquid This will cause the liquid at the condenser s bottom to lose heat faster causing more condenser subcooling In this example high condenser subcooling is not caused from an amount of liquid being backed up in the condenser but from the liquid in the condenser s bottom simply losing heat faster This phenomenon happens because the temperature difference between the liquid at the condenser s bottom and the surrounding ambient is the driving potential for heat transfer to take place As more and more air is restricted from flowing through the condenser the amount of condenser subcooling will increase Notice that the system check sheet shows higher than normal condenser subcooling of 15 This system check sheet looks very similar to an over charge of refrigerant because of the increased subcooling amounts but do not be fooled by it When a high head pressure and high condenser subcool ing is experienced in a refrigeration system the service technician must not assume an overcharge of refrigerant The technician must first check to see if the condenser is dirty or a condenser fan is inoperative because of simi Table 2 System With A Dirty Condenser Item to be measured Measur
46. her the system has compressor superheat and doesn t have compressor superheat both the suction line and compressor s head would still be frosted This is why it is of utmost importance for service technicians to measure superheat at both the evaporator and compressor to make sure the compressor is protected from slugging and flooding Measuring Compressor Total Superheat In review compressor superheat or total superheat is all of the superheat in the low side of the refrigeration system Compressor superheat consists of evaporator superheat and suction line superheat A service technician can www achrnews com Y fink the N EWS measure total superheat by placing a thermometer thermocouple or thermis tor at the compressor inlet and taking the temperature A pressure reading will also be needed at this same location For example consider the example below for a R 404A system with a low side pressure taken at the compressor of 21 psig or 13 and a compressor inlet temperature of 27 The pressure gauge reading on the low side of the system of 21 psig tells the service technician that there is a 13 evaporating temperature The compressor superheat calculation is as follows Compressor inlet temp Evaporator temp Compressor superheat 27 F 13 F 40 F In this example the compressor superheat is 40 It is possible to have a TXV adjusted to control the proper amount of evaporator superheat at the coil and st
47. id refrigerant being boiled off is under the oil in the crankcase very small oil particles will be entrained in this vaporization process The oil level in the crankcase will now drop and rob mechanical parts of vital lubrication Often refrigerant cooled semi hermetic compressors have check valves locat ed on a partition between the crankcase and motor barrel to prevent oil and lig uid refrigerant from mixing Air cooled semi hermetic compressors and hermetic compressors are often more prone to flooding Suction accumulators can help a flooding condition but if the situation is severe accumulators can also flood Crankcase pressures can become excessively high from liquid refrigerant boiling in the crankcase These high crankcase pressures can cause refriger ant and entrained oil particles to escape around the rings of the pistons during its down stroke Once in the compressor s cylinders the refrigerant and oil www ee com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor will be pumped by the compressor into the discharge line The compressor is now pumping oil and refrigerant and robbing the crankcase of lubrication Oil in the system and not in the crankcase will coat the inner walls of the tubing and valves and cause unwanted inefficiencies Higher than normal crankcase pressures Caused from the higher density refrigerant and oil mixture being pumped through the compressor s cylinders will cause hi
48. igher head pressures and lower suction pressures are experienced TXV remote bulbs may not sense the cor rect refrigerant temperature at the evaporator outlet causing improper su perheat control TXV hunting can also occur If an oil separator isn t employed the compressor often sees slugs of oil that are returning from the evaporator The compressor s pistons can mo mentarily pump slugs of liquid oil which can build tremendous hydraulic forces because of the incompressibility of most liquids Serious compressor valve and drive gear damage can result How Helical Oil Separators Work Helical oil separators offer 99 to 100 percent efficiency in oil separation with low pressure drop Upon entering the oil separator the refrigerant gas and oil fog mixture encounter the leading edge of a helical flighting The gas oil mixture is centrifugally forced along the spiral path of the helix causing the heavier oil particles to spin to the perimeter where impingement with a screen layer occurs This screen layer serves as an oil stripping and draining medium The separated oil now flows downward along the boundary of the shell through a baffle and into an oil collection area at the bottom of the sepa rator The specially designed baffle isolates the oil collection and eliminates oil re entrainment by preventing turbulence Virtually oil free refrigerant gas exits the separator through an exit screen just below the lower edge of the helical flightin
49. il that gets past the compressor and into the system not only robs the compressor s crankcase of vital lubrication but it coats the walls of the con denser and evaporator Oil films on the walls of these important heat exchang ers will reduce heat transfer The condenser will not be able to reject heat as efficiently as it should with an oil film coating its walls Even though this oil www is com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor film will be hotter and thinner than if it were in the evaporator system effi ciencies will suffer Head pressures will rise causing higher compression ratios and lower volumetric efficiencies with lower than normal system capacities Oil that coats the walls of the evaporator will decrease heat transfer to the refrigerant in the evaporator A film of oil bubbles which acts as a very good insulator will form on the inside of the evaporator The evaporator will now see a reduced heat load which will cause the suction pressure to be lower Lower suction pressures cause higher compression ratios and lower volumetric effi ciencies The result is a lower system capacity with much longer running times Most metering devices including thermal expansion valves TXV and cap illary tubes will also experience inefficient performance due to the presence of oil filming Capillary tubes may experience wide variation in flow rates Usually reduced refrigerant flow rate with h
50. ill return liquid refrigerant to the compressor at certain low load conditions It is recommended that all TXV controlled refrigeration systems have some compressor superheat to ensure that the compressor does not see liquid refrigerant flood or slug at low evaporator loads The TXV however should be set to maintain proper superheat for the evaporator This will en sure that the compressor will always see refrigerant vapor and not liquid e Book HVACR Service and Troubleshooting With The Professor Oil entrained suction gas i W ers p 7 ANN iit NANN ax mm Figure 3 Refrigerant cooled semi hermetic compressor Figure from Troubleshooting and Servicing Modern Air Conditioning and Refrigeration Systems by John Tomczyk www as com Y fink THE STANDARD IN HVACR BY ANY GE YELLOW JACKET has been manufacturing HVACR tools and equipment that stand the test of time for over 60 years Made in the U S A and engineered to the most exacting standards so you can get the job done right To learn more visit yellowjacket com Looking to sharpen your skills get more out of your tools or share a thought with the HVACR community Visit YJU an academic inspired website packed with resources for HVACR technicians of all skill levels ENGINEERED TO BE THE BEST the NEWS e Book HVACR Service and Troubleshooting With The Professor Ice Flake Machine Troubleshooting any ice flake ma
51. inding or electrical coil can be checked with a megger A megohmmeter s main function is to detect weak motor winding insulation and to detect moisture accumulation and acid formations from the motor windings to ground before they can cause more damage to motor winding insulation When dealing with HVACR hermetic and semi hermetic compressor mo tors as contaminants in the refrigerant and oil mixture increase the electri cal resistance from the motor windings to ground will decrease Because of this regular preventative maintenance checks can be made with a megohm meter and can signal early motor winding breakdown from a contaminated system when accurate records are kept One probe of the megger is connected to one of the motor winding ter minals and the other probe to the shell of the compressor ground Note Make sure metal is exposed at the shell of the compressor where the probe is attached so that the compressor s shell paint is not acting as an insulator to ground When a button is pushed and held on the megger it will apply a high dc voltage between its probes and measure all electrical paths to ground It is important to disconnect all wires from the compressor motor terminals when megging a compressor motor Required Condition Required preventive maintenance Percent reading indicated of winding megohms in field Over 100 Excellent None 30 100 50 Some moisture Change filter drier 35 present 50 20 Severe Several
52. ing With The Professor System Check Sheets his chapter compares subcooling amounts in a refrigeration system incorporating an overcharge of refrigerant a dirty con denser and air in the system Note that all of the system check sheets used as samples in this chapter incorporate R 134a as a refrigerant These systems are refrigeration systems with a thermostatic expansion valve TXV as a metering device with receivers Overcharged System Table 1 shows an R 134a refrigeration system with an overcharge of re frigerant Notice the 30 degrees of liguid subcooling backed up in the con denser Because of the overcharge of refrigerant the condenser will have too much liguid backed up in its bottom causing high condenser subcooling By overcharging a system with too much refrigerant increased liguid subcooling amounts will be realized in the condenser However just because a system has increased subcooling amounts in the condenser doesn t necessarily mean the system is overcharged This will be explained in the next two system checks Remember the condenser is where refrigerant vapor is condensed and liguid refrigerant is formed This backed up subcooled liquid at the condenser s bottom will take up valuable condenser volume leaving less volume for desuperheating and condensation of refrigerant vapors Too much liquid subcooling at the condenser s bottom will cause unwanted inefficiencies by raising the head pressure and the compressi
53. ipitates and will act as a powerful cathodic cor rosion inhibitor It will greatly slow the corrosion process by blocking the reception of electrons that are thrown off by the corrosion process With no place for the electrons to go the corrosion process is physically very ef fectively controlled www 0 com Y fink the N EWS e Book HVACR Service and Troubleshooting With The Professor Loss of Air Conditioning Cooling or this chapter I want to discuss a real life situation regarding poor cooling in a residence and reduced airflow coming from the registers in the house The air conditioner is a three ton 36 000 btuh HCFC 22 split type air conditioner with the A coil in the plenum of the furnace located in the basement The evaporator has an orifice for a metering device The condensing unit is located on the east end of the house The residence is a 1 800 square foot ranch house lo cated in a subdivision in Flint Mich The homeowners are an elderly couple and rely on air conditioning for health reasons It has been an unseasonably hot summer and temperatures in the house are reaching 80 F In fact the homeowners said that temperatures inside the house have been rising steadily in the last two weeks They try to keep the house at 72 throughout the entire summer They are also complaining of high humidity inside the house A service technician soon arrives After introducing himself and his com pany the technician
54. ll Condenser Check Valve V Receiver 4 Figure 1 The Close on Rise of Outlet CRO valve is located between the compressor s discharge line and the receiver inlet All artwork courtesy Sporlan Division Parker Hannifin Corp Compressor through the CRO valve serves to warm up any cold liquid coming from the ORI valve at the receiver s inlet and it will also increase the pressure of the receiver so metering devices will have the proper liquid line pressure feeding them One of the main advantages of condenser flooding is to keep consistent liq uid pressure feeding the metering device in low ambient conditions Manufac www oie com Y fink Figure 2 One way to reduce the A 12D9B SC amount of extra refrigerant charge SpitGondenesr Vaie needed for condenser flooding is to split the condenser into separate and identical condenser circuits ORIT 15 Head Pressure Control Valve Oil Differential Pressure Valve CROT 12 65 225 Head Pressure Control Valve ME 345290 Liguid Line Oil Filter Solenoid Valve Replaceable FY Cateh Al SORIT Suction Throttling a Valves SORIT H i Liquid Line Suction Throttlin 3 Suction Header CE Valves 9 JE tT _ Solenoid Valve Distrib tor THIS SYSTEM DIAGRAM HAS BEEN DEVELOPED ONLY TO ILLUSTRATE SPECIFIC SPORLAN PRODUCTS AND THEIR TYPICAL APPLICATION THE DIAGRAM IS NOT INTENDED AS A PIPING DRAWING AND OR RECOMMENDATION 17 www achrnews com
55. loat an oil return needle is opened and the oil is returned to the compres high side pressures www se com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Chemical Free Cooling Tower Treatment ure water is a rare commodity Water as we know it contains many dissolved miner als When evaporation occurs in a cooling tower only the water evaporates it exits the cooling tower as water vapor but leaves the minerals behind to concentrate in the cooling tower s water system The concentrations of these dissolved minerals gradually increase until a process called precipitation occurs Precipitation happens when dissolved miner als such as calcium carbonate limestone reach a cer tain concentration and become solid usually clinging to equipment and piping surfaces in the cooling tower HVACR personnel refer to these solids as scale Tiny suspended particles exist in large quantities in all city water or well water that is used for cool ing tower or boiler makeup water Once in the cooling tower water system these suspended particles neither sink nor float because of their small size They are transported by the flowing water The particles will concentrate during the evapora tion process and be attracted to the equipment sur faces in the cooling tower When the concentration is so great that the water can hold no more minerals they are forced to find surfaces to precipitate to as
56. merica High Water Levels If the float mechanism in the water reservoir is adjusted wrong or the seat in the float chamber is leaking and the water level is too high the freezing cylinder will experience high water levels This will cause stress on the gear motor from the auger doing more work because there is more surface area of ice to cut Again the overload may trip on the gear motor When the gear motor s overload reset but ton must be reset often a service technician should suspect water level problems as a possible cause Often high water levels will cause water to pour over into the ice storage bin and cause a large melting depression in the stored flaked ice Also this new water constantly coming into the freezing cylinder will impose extra heat load on the evaporator and cause higher than nor mal evaporating pressures and poor ice quality and quantity This happens because the higher quantities of new water will have to be refrigerated to the freezing point to start making ice 27 www achrnews com w fin Figure 3 Water logged shaved ice is carried through the water to the top or head of the freezing cylinder where it is squeezed extruded shaped cut and eventually falls to an insulated ice storage bin for use Courtesy of Ferris State University the NEWS ke Book HVACR Service and Troubleshooting With The Professor More Ice Flake Machine Troubleshooting his chapter is part two of our discussion on ice fl
57. ms a protective canopy to protect the bacte ria beneath it from chemical biocides It is very slimy to the touch four times more insulating to heat transfer than mineral scale and is the primary cause of microbial influenced corrosion on eguipment The bacteria that live in a biofilm and adhere to the equipment surfaces are called Sessile bacteria they represent 99 percent of the total bacteria in a system However this slime layer can be eliminated through a process of nutrient limitation The suspended particles in the water of a cooling tower incorporate most of the free floating planktonic bacteria Normally since like charges repel one another the bacteria are repelled by the suspended particles in cooling tower water due to the fact that nearly all tiny particles have similar negative static electrical charges on their surfaces However after being activated by the high frequency electrical pulse field at the water treatment module by the signal generator the natural electrical static charge on the particle s surface is removed The repulsion to the bacteria is eliminated therefore the bacteria are attracted to the powder and become entrapped in it The powder in effect sweeps the water clean of planktonic bacteria and renders them incapable of reproducing This process is referred to as encapsulation The high frequency pulsing action of the signal generator also damages the membrane of the planktonic bacteria by creating small
58. n to determine the low pressure control s settings Figures 1 and 2 both shown on the previous page show an automatic pump down circuit and system in both schematic and pictorial forms respectively It is important not to let the low side pressure get too low before shutting off the compressor If the low side pressure was allowed to drop to O psig before the low pressure control terminated the cycle every off cycle damage could occur to the compressor from lack of refrigerant mass flow rate and high compression ratios This severely unloads the compressor and may cause overheating from loss of the cooling effect on the compressor s windings A cutout pressure of 10 psig is low enough to ensure most of the liquid and vapor refrigerant has been cleared from the evaporator suction line and crankcase to prevent refrig erant migration during the off cycle www eu com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Flooding and Slugging VACR field service terminology is often confusing and misused even by the most seasoned service veterans Clarification of terminology among service technicians is of utmost impor tance in order to clarify the real problem and efficiently find the correct remedy Clear concise and accurate communica tion between service technicians part suppliers customers and the home shop is rapidly gaining importance as the HVACR field transitions become more technically
59. nd the oxygen in the air will oxidize the systems oil rapidly In a closed system pressure from the oxidizing oil can build up rapidly and may generate pressures to a point of exploding The second step in testing for pressure depen dent leaks is to always conduct proper bubble testing by thoroughly saturating all surfaces with a micro foam solution Allow up to 15 minutes reaction time for the microfoam to expand into a visible white co coon structure Figure 1 and Figure 2 shown on the next page Use an inspection mirror to view any undersides and a light source for dark areas Third starting at the compressor coat all sus pected surfaces Continue to coat all suction line connections back to the evaporator section Fourth spray coat all fittings starting at the discharge line at the compres sor to the condenser coil Spray coat all soldered condenser coil U joints Fifth from the condenser continue to spray coat all liquid line connections including the receiver valves seams pressure taps and any mounting hard ware Continue the liquid line search back to the evaporator section Sixth any control line taps to the sealed system must be spray coated the entire length of their run all the way back to the bellow device Seventh expose the evaporator section and coat all connections valves www si ae com Y fink the Figure 2 Proper bubble testing for leaks includes thoroughly saturating all surfaces Pho
60. nt on new start ups Testing for Evaporator Section Leaks Many leaks that go undetected are in the evaporator coil This is because most evaporator sections are contained in cabinets buttoned up or framed into areas that do not allow easy access In order to avoid time consuming labor to strip off covers ducting blower cages or the unloading of product an easy electronic screening method is outlined on the next page www a com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor Figure 2 Oil is always present at Schrader valves and access ports due to the discharging of refrigerant hoses on the manifold gauge set Photo courtesy of Refrigeration Technologies Anaheim Calif 1 Turn off all system power including evaporator fan motors 2 Equalize high and low side pressures in the refrigeration or air condi tioning system and defrost any frozen evaporator coils If the system does not have any pressure evacuate to the required levels and then add a refrigerant trace gas Nitrogen is then added to generate a practical test pressure Most low sides of systems have a working pressure of 150 psig but always read the nameplate on the evaporator section for test pressure specifications 3 Calibrate an electronic leak detector to its highest sensitivity 4 Locate the evaporator drain outlet or downstream drain trap 5 Position the electronic leak detector probe at the drain opening Be car
61. on ratio Higher compression ratios cause lower volumetric efficiencies and lower mass flow rates of refrigerant through the refrigeration system Higher superheated Table 1 Overcharged System Item to be measured Measured value Compressor discharge temperature 240 F Condenser outlet temperature 90 F Evaporator outlet temperature 15 F Compressor inlet temperature 258 Ambient temperature 0 E Box temperature PON Compressor volts 230 V Compressor amps High Low side evaporator pressure 8 8 psig 5 F High side condensing pressure Item to be calculated Calculated value 172 psig 20 TF Condenser split DO Condenser subcooling 60 FE Evaporator superheat KOE Compressor superheat ZOE compressor discharge temperatures will also be realized from the higher heat of compression caused from the high compression ratio Remember most conventional condensers functions are to e Desuperheat compressor discharge vapors www ee com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor e Condense these vapors to liquid and e Subcool refrigerant at its bottom System with Dirty Condenser Table 2 shows a refrigeration system with a dirty condenser causing restricted airflow over the condenser A similar condition would be a de fective condenser fan motor starving the condenser of air Both conditions caused the head pressure and thus condensing temperature to increase Even the liquid at t
62. ondenser circuits Figure 2 on the previous page This method is referred to as condenser splitting The splitting way where only one half of the condenser is used for winter operation and flooding section of this chapter both halves are used for summer operation The top half of the condenser is In fact during winter operations the system s head pressure is best main referred to as the summer winter condenser and the bottom half of the con tained with a combination of condenser splitting refrigerant side head pressure www 00 com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor controls and air side controls like fan cycling or fan variable speed devices This combination of refrigerant side and air side controls will minimize the re frigerant charge even more while splitting the condenser These combinations will also maintain the correct head pressure for better system efficiencies The refrigerant that is trapped in the idle summer condenser during low ambient conditions will flow back into the active system through a bleed hole in the piston of the three way valve This trapped refrigerant will flow through the piston s bleed hole into the valve s pilot assembly and back to the suction header through a small copper line which feeds all parallel com pressors Figure 2 Another scheme to rid the idle summer condenser of its refrigerant is to have a dedicated pump out solenoid valve
63. ontaminate the deli cate detection tips of electronic detectors There are six classifications of leaks 1 Standing leaks Standing leaks are leaks that can be detected while the unit is at rest or off This includes freezer evaporator coils warmed up by defrost Standing leaks fortunately are the most common of all leaks 2 Pressure dependent leaks Pressure dependent leaks are leaks that can only be detected as the system pressure increases Nitrogen is used to pressurize the low sides of systems to around 150 psig and high sides to 450 psig Never use air or pure oxygen Often a refrigerant trace gas is introduced into a recovered and evacuated system along with the nitrogen The trace gas enables electronic leak detectors to be used to detect the vicinity of the leak Refrigerant trace gas will be covered in more detail later in the article Pressure dependent leak testing should be performed if no leaks are discovered by the standing leak test Bubbles or a microfoam solution can also be used to locate pressure dependent leaks Warning Mixtures of nitrogen and a trace gas of refrigerant usually of the system s refrigerant can be used as leak test gases because in these cases the trace gas is not used as a refrigerant for cooling However a technician cannot avoid recovering refrigerant by adding nitrogen to a charged system Before ni trogen is added the system must be recovered and then evacuated to appropriate www 00 com
64. or as low as 1 ounce every 10 years Every pressurized system leaks because flaws exist at every joint fitting seam or weld These flaws may be too small to detect with even the best of leak detection equipment But given time vibration tempera ture and environmental stress these flaws become larger detectable leaks It is technically incorrect to state that a unit has no leaks All equipment has leaks to some degree A sealed system which has operated for 20 years without ever needing a charge is called a tight system The equipment still has leaks but not enough leakage to read on a gauge or affect cooling perfor mance No pressurized machine is perfect A leak is not some arbitrary reading on a meter Gas escapes at different times and at different rates In fact some leaks cannot be detected at the time of the leak test Leaks may plug and then reopen under peculiar conditions A leak is a physical path or hole usually of irregular dimensions The leak may be the tail end of a fracture a speck of dirt on a gasket or a microgroove between fittings Exposing the Leak Refrigerant vapor can flow under layers of paint flux rust slag and pipe insulation Often the refrigerant gas may show up quite a long distance from the leak site This is why it is important to clean the leak site by removing loose paint slag flux or rust Remove any pipe insulation Oil and grease must also be removed from the site because they will c
65. oriented The previous chapter on refrigerant migration discussed how this issue can damage the compressor s mechanical parts It also covered remedies to migration using automatic pump down systems This chapter will cover flood ing and slugging of compressors Two important service terms that are often misunderstood and misused by service technicians are flooding and slug ging Each one will be thoroughly defined and explained as they apply to refrigeration and air conditioning compressors Flooding Flooding is liquid refrigerant entering the compressor s crankcase while the compressor is running Flooding occurs to a compressor only during the on cycle Causes could be e Wrong TXV setting no compressor superheat e Overcharge e Evaporator fan out e Low load on evaporator e End of cycle lowest load e Defrost clock or heater out iced coil e Dirty or blocked evaporator coil e Capillary tube overfeeding e Capillary tube system overcharged e Expansion bulb loose on evaporator outlet e Oversized expansion valve e Flooding after hot gas termination e Heat pump changeover and e Defrost termination Since liquid refrigerants are heavier than refrigeration oils liquid refriger ant returning to the compressor will settle under the oil in the bottom of the compressor s crankcase This liquid refrigerant will gradually be boiled off from the low pressures in the crankcase However since the liqu
66. pores in their outer membrane The condition weakens the bacteria and inhibits their capabilities to reproduce This process is referred to as electroporation Microbial life has a 24 to 48 hour life span Any microbe not captured in the forming powder are zapped by the secondary pulse of the signal generator forcing them to spend their lives repairing cell wall damage rather than reproducing All of the living organisms in a cooling tower system depend on one anoth er for their food supply Thus when the nutrients from the planktonic bacteria are diluted by both encapsulation and electroporation the biofilm cannot be sustained and it will disintegrate The biofilm will never be created if the cooling tower system is installed using a high frequency electrical pulse field and creating encapsulation and electroporation processes The combined effects of encapsulation and elec troporation result in exceptionally low total bacterial counts TBC in cool ing tower water Corrosion Control Most corrosion in cooling tower systems or boilers comes from e Chemical additives e Softened water Biofilm and e Mineral scale So by removing chemicals avoiding the use of softened water and using the chemical free water treatment module and signal generator in cooling tower and boiler water applications corrosion concerns can be eliminated The calcium carbonate that coats the suspended particles is in a state of saturation while it prec
67. quid backed up in the con denser causes a reduced condenser internal volume and raise condensing pressures Now that the condensing pressures are raised there is more of a temperature difference between the surrounding ambient and condensing temperature causing greater heat flow This compensates for the reduced condenser s internal volume The system will still reject heat but at a higher condensing pressure and temperature High Condenser Splits Because of the higher condensing pressures thus higher condensing temperatures there will be a greater temperature difference split between the ambient and condensing temperature A dirty condenser will also give a system high condenser splits but the condenser subcooling will not be as high as with an overcharged system Normal to High Evaporator Pressures Since this system has a TXV metering device the TXV will still try to maintain its evaporator superheat and the evaporator pressure will be normal to slightly high depending on the amount of overcharge If the overcharge is excessive the evaporator s higher pressure would be caused by the decreased mass flow rate through the com pressor from high compression ratios causing low volumetric efficiencies The evaporator would have a harder time keeping up with the higher heat loads from the warmer entering air temperature The TXV will also have a ten dency to overfeed refrigerant to the evaporator on its opening stroke due to the high hea
68. r outlet temp sccccccssssecececeeeeeeeeees 75 Evaporator outlet temp ccccsssssesccceeesseeeeeeeees 25 Compressor in tOMP ccccccsceesssssesecceeecceeceeeeeees 55 Ambient temperature cccccsssseseeceeeeseeeeeeeeees 75 Box temperature ccccsssscecccccesssscceseessescceseees 25 Compressor volts cccccccccceeesssssesecececceeeeeeeeees 230 Compressor GINS sicscssiausssatascrzeccvasennseidacessavedseinsess low Lowside evaporating pressure psig 1 6 psig 10 Highside condensing pressure psig 95 psig 85 Calculated values F Condenser Split cccccceccccecessssseseecceeceeeeeeseeees 10 Condenser subcooling ccecccssecceeescesscceeceeeess 10 Evaporator Superheat ccccsssssseeccceessseeceeeeeees 15 Compressor SUperheat cccseessseeeeeccceceeeeeesseeees 45 www ee ie com Y fink the NEWS e Book HVACR Service and Troubleshooting With The Professor Symptoms include e Higher than normal discharge temperatures e Low condensing head pressures and temperatures e Normal to high condenser subcooling e Normal to high superheats e High evaporator suction pressures and e Low amp draw Higher than normal discharge temperatures A discharge valve that isn t seating properly because it has been damaged will cause the head pres sure to be low Figure 1 Refrigerant vapor will be
69. rant flow from the compressor s discharge line to the three way valve s inlet port and then equally to the valve s two outer ports In other words the flow of refriger ant will flow to both of the condenser halves egually In low ambient conditions the summer portion of the condenser can be taken out of the active refrigeration system by the three way valve When the coil of the pilot operated three way solenoid valve is energized the sliding piston inside the valve will move and close off the flow of refrigerant to the port on the bottom of the valve that feeds the summer condenser This action will render the summer condenser of the condensers is done with the addition of a pilot operated three inactive or idle and the minimum head pressure can be maintained by way solenoid valve installed in the discharge line from the compressors flooding the summer winter half of the condenser with conventional re Figure 3 The splitting of the identical condensers is done in such a frigerant side head pressure control valves as explained in the condenser Condenser Splitting As mentioned above the main disadvantage of condenser flooding is that larger refrigeration sys tems may hold hundreds of extra pounds of refriger ant needed to properly flood a condenser at extremely low ambi ent conditions One way to reduce the amount of extra refrigerant charge needed for condenser flooding is to split the condenser into two separate and identical c
70. s distributed to each compressor s oil level regulator at a reduced pressure before entering a compressor s crankcase www 00 com Y fink the N EWS e Book HVACR Service and Troubleshooting With The Professor Frost on the Compressor s Head any service technicians believe that if there is frost on the compressor s head there is cause for alarm This is sim ply not true Frost is simply frozen dew Usually on lower temperature refrigeration applications the suction line and part of the compressor s head will get cold The part of the compressor s head that gets coldest is where the suction vapors enter before they are compressed These parts often get cold enough to reach the dew point of the surrounding air When the air s dew point temperature is reached from coming in contact with the cold suction line and compressor head water vapor in the air is cooled to its dew point and will condense on the suction line and head of the compressor When this condensed water vapor reaches 32 F it will freeze into frost Figure 1 So frost is simply condensed water vapor or dew which has reached 32 or below System Specifications Consider a low temperature commercial refrigeration application operating with 7 of evaporator superheat and 40 of compressor superheat Figure 2 page 23 The refrigerated box temperature is 0 with an evaporator tempera ture of 13 It is an R 404A system With an evaporator
71. service person manually resets the overload on the gear motor Cleaning the ice flake machine according to the manufacturer s recommendations with an Figure 1 The ice cutting auger drive train with gears and the gear motor are all connected Courtesy of Ferris State University approved cleaner and inspecting the bearings connecting the cutting auger with the drive train will prevent mineral buildup on the freezing cylinder s surface and keep the ice flake machine operating quieter and longer Often grease can leak out of a bearing housing and start a bearing failure If a bearing has started to fail the cutting auger may wobble from the added clearance in the worn bearing This wobbling as the auger rotates may cause the auger to touch the freezing cylinder evaporator and scar its surface If www ae com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor scarring of the evaporator surface or auger s cutting surface has occurred one of the components will for sure have to be replaced Always follow the manufacturer s recommendation when replacing a cutting auger or freezing cylinder It is this gear motor assembly that is more susceptible to failure than any other part of the ice flake machine Remember as the auger rotates and cuts ice and mineral deposits the gear motor and gear assembly senses all of these stresses and strains It is for this reason that some manufacturers have manufac
72. t its bottom Condenser Split 50 causing high head pressures All of the heat being absorbed in the evaporator Condenser Subcooling 30 and the suction line along with motor heat and high heat of compression from Evaporator Superheat 20 the high compression ratio has to be rejected into a smaller condenser s inter Compressor Superheat 10 nal volume because of the backed up overcharged liquid refrigerant www senna com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor High Condenser Subcooling Because of the overcharge of refrigerant in the system the condenser will have too much liguid backed up at its bottom causing high subcooling Remember any liguid in the condenser lower than the condensing temperature is considered subcooling You can measure this at the condenser outlet with a thermometer or thermocouple Subtract the condens ing out temperature from the condensing temperature to get the amount of liquid subcooling in the condenser A forced air condenser used in refrigeration should have at least 6 8 of liquid subcooling in the condenser However sub cooling amounts do depend on system piping configurations and liquid line static and friction pressure drops Condenser subcooling is an excellent indicator of the system s refrigerant charge The lower the refrigerant charge the lower the subcooling The higher the charge the higher the subcooling High Condensing Pressures Subcooled li
73. temperature of 13 and the system having 40 of compressor superheat the temperature of the re frigerant coming into the compressor is 27 13 plus 40 The 27 temperature coming into the compressor is lower than the surrounding air s dew point and it is also lower than the freezing point of water 32 so the dew on the suction line and compressor s head will form frost These frost lines are com pletely normal for this low temperature application refrigeration machine Figure 1 Condensed water vapor freezes into frost Courtesy of Ferris State University Compressor Flooding or Slugging Because the system has a compressor superheat of 40 there is no worry about whether the compressor is flooding or slugging In review flooding is liq uid refrigerant coming back to the compressor s crankcase during a run cycle Slugging is liquid refrigerant or oil actually entering the compressor s cylinders and or valve arrangement and being pumped Again because the system has superheat at the compressor of 40 flooding and slugging cannot exist www us com Y fink the N EWS Mostly liquid with some liquid flashing to vapor Metering device 6 100 liquid ne Evaporator i j id id V Receiver Filter drier Condenser Compressor Mo Figure 2 Low temperature commercial refrigeration application Figure from Troubleshooting and Servicing Modern Air Condi
74. the ke Book Published September 2012 y N j j v V N j j V N M y A N N v V 4 i N V y 4 N f gt V I 7 SERVICE TROUBLESHOOTING A bn PUBLICATION By John Tomczyk the N EWS Contents Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 System Check Sheets cssscscssssssssssssssssccsssssnessesssssesecssssseees 5 Megohmmeters for Preventive Maintenance 6 Bad Compressor Valves w sssssssssssssssssssssssssessccsssssnesssessssseses 8 Chemical Free Cooling Tower Treatment n Loss of Air Conditioning Cooling 14 Condenser Splitting sssssssscsssssssssesssssssssssssesessssssssssneseseessee 16 Helical Oil Separators soka ser duhkuu ikdol tattoo 20 Frost on the Compressor s Head vcscssssessscessssessssssssnees 22 Ice Flake Machine Troubleshooting 26 More Ice Flake Machine Troubleshooting 28 Restricted TXV Metering Device een 30 Basic Leak Detection Methods 33 Advanced Leak Detection eee 37 Checking on Refrigerant Overcharge reese 4 Refrigerant Migration 45 Flooding and st 0 4 111 eee eRe eR Men ee oem eee 46 e Book HVACR Service and Troubleshooting With The Professor About The Author ohn Tomczyk is co author of the book Refrigeration and Air Conditioning Tech nology published by Delmar Cenga
75. till cooling but not cooling to its rated capacity The medium temperature products will spoil guicker and the low temperature products are not frozen as solid as they should be There are three main reasons why a compressor will simultaneously have a low head pressure and a high suction pressure e Bad leaky compressor valves Figure 1 e Worn compressor rings Figure 2 and e Leaky oil separator Leaky Compressor Valves Here are reasons why a compressor s valves may become inefficient be cause of valve warpage from overheating or lack of lubrication or from having carbon and or sludge deposits on them preventing them from sealing properly e Slugging of refrigerant and or oil e Moisture and heat causing sludging problems e Refrigerant migration problems e Refrigerant flooding problems e Overheating the compressor which may warp the valves e Acids and or sludges in the system deteriorating parts e TXV set wrong Too little superheat causing flooding or slugging e TXV set wrong Too much superheat causing compressor overheating e Undercharge causing high superheat and compressor overheating and e Low load on the evaporator from a frozen coil or fan out causing slug ging or flooding of the compressor Below is a service checklist for a compressor with valves that are not sealing Compressor With Leaky Valves Measured Values Compressor discharge temp sceccccecceeeseeees 225 Condense
76. tioning and Refrigeration Systems by John Tomczyk 23 ke Book HVACR Service and Troubleshooting With The Professor In order for slugging or flooding to occur the compressor would have to be experiencing no superheat In other words the temperature coming into the compressor would be the same as the evaporator temperature 13 This would indicate that there was no compressor superheat and liquid refrigerant was entering the compressor The amp meter on the air cooled semi hermetic compressor Figure 1 is reading 5 87 amps The rated load amps RLA of the air cooled semi hermetic compressor is 6 5 amps We are still quite below the RLA of the com pressor However if liquid was coming back to the compressor the amp meter would be above the RLA rating of the compressor A mixture of high density vapors and liquid is hard for the compressor to pass causing high amp read ings Valve plate damage usually occurs in these situations Air cooled semi hermetic compressors bring the refrigerant gas right back to the head of the compressor and then to the suction valves directly This is why it is very impor tant to have some superheat to ensure that vapor and not liquid is returning to the compressor This is not the case for refrigerant cooled compressors where suction gases come into the end bell of the compressor and then pass through the motor windings before entering the valve arrangement Figure 3 page 24 In either scenario whet
77. to courtesy of Refrigeration Technologies Anaheim Calif and U joints Notice that the first sequence of searching started with the compressor and suction line due to their large surface areas The next sequence began with the discharge line went across the condenser to the liquid line connection and then to the evaporator section The evaporator section is the last and least desirable component to pressure test in the field Temperature Dependent Leaks The third classification of leaks is temperature dependent All mechanical connections expand when heated The connections on refrigeration and air con ditioning systems are usually of soft metals such as copper brass or aluminum Figure 3 An example of a micro foam solution used for leak testing Photo courtesy of Refrigeration Technologies Anaheim Calif ke Book HVACR Service and Troubleshooting With The Professor These metals actually warp when heated then contract and seal when heat is removed The procedures to deal with that are 1 Place the unit in operation and raise the operating temperature by partially blocking the condenser s air intake Warm water may also be used for system pres surization Water chillers are usually pressurized using controlled warm water When dealing with chillers valve off the condenser and evaporator water circuits Controlled warm water is now intro duced on the evaporator tube bundle This causes the rate of vaporization o
78. tured open type gear case housing assemblies This means the gear assembly has a vent and is ex posed to the atmosphere usually with a soft plastic plug holding the gear lube grease from escaping When excessive heat occurs from gear motor stress expanded hot grease can escape through the vent However one has to be careful to keep the vent hole plugged or moisture can enter This will deterio rate the lubricating effect of the grease and excessive gear wear will result Usually a regular clicking sound will be heard from the drive train if a gear is chipped from poor lubrication or too much stress However if the auger motor is starting to fail a loud higher pitch noise will be heard Cleaning the ice flake ma chine with an approved cleaner and inspecting the bearings connecting the cutting auger with the drive train will prevent mineral buildup on the freezing cylinder s surface and keep the ice flake machine operating quieter and longer www a ie com Y fink the N EWS e Book HVACR Service and Troubleshooting With The Professor Restricted TXV Metering Device his chapter explores how a restricted metering device will affect system performance and efficiency The system is a commercial refrigeration system with a TXV as the metering device The refrigerant being used is HFC 134a Very similar results will occur if an automatic expansion valve AXV is used However because different refrigerant system confi
79. ually trying to be compressed in the cylinders of the compressor Slugging happens during the compressor s on cycle As we know liquids cannot be compressed and tremendous reversal forces are generated often resulting in broken parts Slugging can especially happen if the compressor is located in a cold ambient outdoor setting The cold ambient will amplify the lower vapor pressure area and help condense the refrigerant vapor to liquid The crankcase heater does help keep the oil in the crankcase free of refrigerant from refrigerant migration Because refrigeration migration can occur with refrigerant vapor the migra tion can occur uphill or downhill Once the refrigerant vapor reaches the crank case it will be absorbed and condense in the oil Refrigerant and oil have a strong attraction for one another and mix very well Since liquid refrigerant is heavier than oil the liquid refrigerant will be on the bottom of the oil in the crankcase On short off cycles the migrated refrigerant does not have a chance to settle under the oil but does still mix with the oil in the crankcase When the compressor does turn on the sudden pressure drop on the crankcase contain ing liquid refrigerant and oil will cause the refrigerant in the oil to flash to a vapor This causes violent foaming in the crankcase The oil level in the crankcase will now drop and mechanical parts will be scored from inadequate lubrication The crankcase pressure will now rise
80. vapor refrigerant from the solenoid forward through the compres sor will be pumped into the high side condenser and receiver of the system Once the low side pressure reaches about 10 psig a low pressure controller will interrupt the compressor circuit initiating an off cycle The system is now pumped down and migration cannot occur because of lack of refrigerant vapor Power line eae Evaporator Thermostat Compressor and motor Low pressure control Figure 2 Pictorial diagram of an automatic pump down system Figure from Troubleshooting and Servicing Modern Air Conditioning and Refrigeration Systems by John Tomczyk and liquid in the evaporator suction line and crankcase When the box thermo stat then calls for cooling the liquid line solenoid is energized refrigerant pres sure will now travel through the metering device to the low side of the system www oe com Y fink the NEWS ke Book HVACR Service and Troubleshooting With The Professor This pressure will cause the cut in pressure of the low pressure control to close its contacts and bring the compressor to another on cycle The cut in pressure for the low pressure control is system and refrigerant dependent It has to be high enough to prevent any short cycling of the compressor during an on cycle but low enough to allow the low side pressure to reach it when the box thermostat initiates an on cycle Actual trial and error will allow a service technicia

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