Honeywell T874G User's Manual
Contents
1. COOL a 4 m an EM HT RELAY eM nr 4h LED A gp SYSTEM cs15a 5R 11 VY LED OUTDOOR z ups 4R GREEN THERMISTOR MN RESET A POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED 5598 4R A REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS pee Fig 6 Internal schematic and typical hookup for T874R Q674L in heat pump system with outdoor reset Includes AUX HT EM HT and SYSTEM LEDs L1 L2 Lo HOT H1 C1 2 A ANTICIPATOR 26 5 VAC TRANSFORMER AUTO on 0 0 4 EM HT RELAY LO 4 EMERGENCY HEAT RED AUXILIARY EM HT HEAT LARA GREEN FAN RELAY CHANGEOVER RELAY HT RELAY COOL COMPRESSOR RELAY aa pee POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED 6565 Fig 7 Internal schematic and typical hookup for T874R Q674L in heat pump system Includes and AUX HT LEDs 69 0268 11 6 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS W3 RELAY COOL CHANGEOVER VALVE COMPRESSOR MONITOR 1 FAN RELAY FAN ANTICIPATOR 9 SWITCH AUTO C ANTICIPA2. THERMOSTAT MOUNTING SLOTS 2 THERMOSTAT MOUNTING POST 2 THERMOSTAT N CAPTIVE MOUNTING M3266 SCREWS 2 Fig 14 Mounting thermostat on subbase SETTING Temperature Setting The T874R has one setpoint lever that controls both heating and cooling The T874G has one lever that controls heating and another lever that controls cooling Move the setpoint lever s to the desired control position s Subbase Setting System switching positions control thermostat operation as follows EM HT Emergency heating system is energized Cooling system is off Compressor is de energized HEAT Heating system is controlled by the thermostat Cooling system is off OFF Both the heating and cooling systems are off COOL Cooling system is controlled by the thermostat Heating system is off AUTO Thermostat automatically changes between heat and cool modes depending on indoor temperature Fan switching positions control fan operation as follows ON Fan operates continuously AUTO Fan operates with equipment as controlled by the thermostat To switch positions use your thumb and index finger to slide the lever to the desired position The switch lever must be set directly over the desired function indicator mark for proper circuit operation CHECKOUT Heating Move the system switch on the subbase to HEAT and the fan switch to AUTO Move the setpoint lever heating lever on T874G on the thermostat
3. oo T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS FALL FAN SWITCH H1 ANTICIPATOR COOL CHANGEOVER AUTO VALVE CHA FAN RELAY B RELAY GENI A o AUX HT RELAY L1 SYSTEM SWITCH EM HT 4 HEAT F4 AUTO F4 COOL EM HT LED RED Eu EM HT RELAY HOT G A AUX HT LED GREEN AUX HT RELAY Ee POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED TERMINAL LABELED C X ON SOME MODELS W3 TERMINAL ON SOME MODELS ONLY COMPRESSOR CONTACTOR M5986A Fig 3 Internal schematic and typical hookup for T874G Q674F in heat pump system Includes AUX HT and EM HT LEDs 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS M COOL CHANGEOVER VALVE FAN SWITCH FAN RELAY Hi NH AUTO FALL ANTICIPATOR ONCE X 3 5 6 IN 6 FALL AUX HT _ LED CH H2 YELLOW H2 ANTICIPATOR SWITCH F RISE EMT Oop AUTO co ort EE o SYSTEM 10 LED GREEN Lag ANTICIPATOR 4 RISE C1 COMPRESSOR 4R POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED
4. CONTACTOR M1629 A REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS Fig 4 Internal schematic and typical hookup for T874G Q674J in heat pump system Includes AUX HT CHECK and SYSTEM LEDs 69 0268 11 4 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS z COOL FAN CHANGEOVER VALVE Hi SWITCH Ci AUTO FALL lof FAN RELAY ON _F 4 u ooe ANTICIPATOR d 12 A 9 gt AUX HT YELLOW s EM HT RELAY SYSTEM SWITCH COMPRESSOR Er FAILURE HTE CHECK JN He LED MAAN 6 RED FALL LY H2 ANTICIPATOR Ss coo FA o Oe O C815A OUTDOOR THERMISTOR E SYSTEM RESET LED GREEN AAA COMPRESSOR A POWER SUPPLY PROVIDE DISCONNECT CONTACTOR MEANS AND OVERLOAD PROTECTION AS REQUIRED 4 1628 FACTORY INSTALLED JUMPER Fig 5 Internal schematic and typical hookup for T874R Q674L in heat pump system with outdoor reset Includes AUX HT CHECK and SYSTEM LEDs 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS COOL CHANGEOVER VALVE FAN RELAY H1 C1 ON ANTICIPATOR 4 AUX HT LED YELLOW A FA 2 ANTICIPATOR
5. H1 C1 ANTICIPATOR FAN SWITCH SYSTEM COMPONENTS AUX HT AUX HT SYSTEM SWITCH EM HT _ LED GRN RELAY wo ExcH FAN RELAY OFF H Q Q O EH ir R cooL HA 4 S v COOL CHANGEOVER VALVE O Eeh EM HT RELAY COMPRESSOR CONTACTOR Lo B RELAY A POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED A TERMINAL LABELED C X ON SOME MODELS A W3 TERMINAL AVAILABLE ON SOME MODELS ONLY M3683A Fig 10 Internal schematic and typical wiring diagram for T874R Q674L in heat pump system Includes EM HT and AUX HT LEDs Mounting the Thermostat Remove the thermostat cover by pulling the bottom edge of the cover outward and away from the base until it snaps free of the retaining posts NOTE The cover is hinged at the top and must be removed by pulling the bottom edge outward and away from the base Carefully remove and discard the polystyrene packing insert that protects the mercury switches during shipment Turn over the thermostat base and note the spring fingers that engage the subbase contacts Make sure the spring fingers are zo bent flat preventing proper electrical contact with the subbase Note the tabs along the top inside edge of the thermostat base The tabs fit into the corresponding slots on the top of the subbase Mount the thermostat on the subbase Q A
6. Honeywell T874G R Multistage Heat Pump Thermostats and Q674F J L Subbases INSTALLATION INSTRUCTIONS APPLICATION The T874G R Thermostats with Q674F J L Subbases provide 24 to 30 Vac control of a two stage heating one stage cooling heat pump system See Table 1 for thermostat subbase specifications Table 1 Thermostat Subbase Specifications T874G Q674F OFF EM HT HEAT AUTO COOL AUTO ON Auto and Manual T874G Q674J EM HT AUTO OFF AUTO ON T874R Q674L EM HT HEAT OFF COOL AUTO ON OPERATION On a two heat thermostat the two stages of heat make sequentially as the temperature drops Make refers to the mercury switch initiating a call for heat or cool There are about 2 F 1 C between stages so that the second stage makes only when the first stage cannot handle the load This is the nferstage differential LEDs light emitting diodes are included on your subbase Refer to the list below for specific meaning The CHECK LED lights when something needs to be checked or done to maintain efficient operation of the system See your heating system instructions for the specific meaning The SYSTEM LED lights when the system is calling for heating or cooling The AUX HT LED lights when the auxiliary heat second stage is operating Auxiliary heat operates when the heat pump alone cannot handle the load The EM HT LED lights when the system switch is placed in the EM HT position Emergency heat is operating in
7. TOR 2 po AUX HT RELAY SYSTEM SWITCH 2 Q E CFI LED GRN EM HT RELAY 5 EA ANTIGIPATOR ace JN H OFF A HEAT FALL 2 CHANGEOVER book VALVE oE W1 RELAY POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD 9 old PROTECTION AS REQUIRED i A remove JUMPER WHEN W1 RELAY IS USED COMPRESSOR i LANFACTORY INSTALLED JUMPER s C M5067 Fig 8 Internal schematic and typical hookup for T874R Q674L in heat pump system Includes CHECK EM HT and AUX HT LEDs 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS HOT L1 12 H1 C1 ANTICIPATOR FAN SWITCH EM HT SYSTEM LED RED MONITOR RD SYSTEM SWITCH Q Q COOL 4 O O A POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED FAN RELAY EM HT COOL CHANGEOVER VALVE oar Eel COMPRESSOR CONTACTOR M5072A A AUXILIARY HEAT LED AVAILABLE ON SOME MODELS Fig 9 Internal schematic and typical hookup for T874R Q674L in heat pump system Includes EM HT and AUX HT LEDs W3 terminal for additional heat stage 69 0268 11 8 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES THERMOSTAT SUBBASE
8. about 10 F 6 C above the room temperature Heating and fan should start if there is no time delay or outdoor temperature limiting system Move the lever heating lever on T874G about 10 F 6 C below the room temperature Heating and fan should shut off Cooling N CAUTION Do not operate cooling if outdoor temperature is below 50 F 10 C Refer to manufacturer recommendations Move the system switch on the subbase to COOL Move the setpoint lever cooling lever on T874G on the thermo stat about 10 F 6 C below the room temperature Cooling and fan should start Move the lever cooling lever on T874G about 10 F 6 C above the room temperature Cooling and fan should stop Emergency Heat Move the system switch on the subbase to EM HT Move the setpoint lever heating lever on T874G about 10 F 6 C above the room temperature The electric strip heater s should come on Move the lever heating lever on T874G about 10 F 6 C below the room temperature The electric strip heater should de energize Fan Move the subbase system switch to OFF and the fan Switch to ON The fan should run continuously When the fan switch is in the AUTO position fan operation is controlled by the heating or cooling system Outdoor Reset Thermistor Some systems are supplied with a Honeywell C815A1005 Thermistor for outdoor mounting The thermistor must be used if not thermostat performance will deviate radically from prope
9. ake care that the wires do not fall back into the wall opening Set aside the subbase Drill four 3 16 in 5 mm holes and gently tap anchors into the holes until flush with the wall WIRES THROUGH WALL OPENING ANCHORS MOUNTING 2 HOLES x MOUNTING M926 SUBBASE SCREWS 2 Fig 2 Installation of subbase on wall Pull wires through the cover plate if used and subbase cable opening See Fig 12 Secure the cover plate if used and subbase with the screws provided Do not fully tighten the subbase screws Level the subbase using a spirit level as shown in Fig 11 and firmly tighten the subbase mounting screws The subbase mounting holes provide for minor out of level adjustments IMPORTANT An incorrectly leveled subbase will cause the temperature control to deviate from setpoint Wiring the Subbase All wiring must comply with local electrical codes and ordinances Follow the equipment manufacturer wiring instructions when available To wire the subbase proceed as follows Connect system wires to the subbase See Fig 3 through 11 A letter code is located near each terminal for identification The terminal barrier permits straight or conventional wraparound wiring connection Fig 13 Firmly tighten each terminal screw Fit wires as close as possible to the subbase Push excess wire back into the hole Plug the hole with nonflammable insulation to prevent drafts from affecting the thermostat
10. et the cover on a table near an accurate NOTE Radiant heat from your hands will offset the thermometer thermometer reading After making each After allowing five or ten minutes for stabilization adjustment wait five or ten minutes for the compare the readings If they are the same replace thermometer to stabilize before comparing cover and put system into operation If they are different recalibrate the thermostat thermometer see step 4 4600 4400 4200 amp 1600 1400 1200 1000 800 600 400 200 gt 4000 C815A THERMISTOR RESISTANCE 5 3800 R 400 ohms 10 77 F 25 uj 3600 3400 3200 t5 3000 2800 2600 tc 2400 2200 2000 gt 1800 20 0 20 40 80 100 120 140 M5070 TEMPERATURE OF THERMISTOR F M1590A Fig 15 Thermistor resistance chart Fig 16 Thermometer calibration Honeywell Home and Building Control Honeywell Inc 1985 Douglas Drive North Golden Valley MN 55422 69 0268 11 J S Rev 12 95 Home and Building Control Honeywell Limited Honeywell Limit e 35 Dynamic Drive Scarborough Ontario MIV 479 Printed in U S A on recycled paper containing at least 1096 post consumer paper fibers www honeywell com yourhome
11. fts from affecting the thermostat operation 3 Do overtighten the thermostat captive mounting screws because damage to the subbase threads can result 4 Do not short across coil terminals on relay this can burn out the heat anticipator Location Install the thermostat about 5 ft 1 5m above the floor in an area with good circulation at room temperature Do not install the thermostat where it can be affected by drafts or dead spots behind doors and in corners hot or cold air from ducts radiant heat from sun or appliances concealed pipes and chimneys unheated uncooled areas such as an outside wall behind the thermostat Mounting the Subbase The thermostat subbase can be mounted on a vertical outlet box horizontal outlet box or directly on the wall VERTICAL COVER ADAPTER PLATE SCREWS 2 HORIZONTAL OUTLET x MOUNTING BOX SCREWS 2 A NOT INCLUDED WITH UNIT A ACCESSORY PARTS AVAILABLE 1931214 M925 Fig 1 Installation of subbase on outlet box 69 0268 11 If you must mount the subbase on a vertical outlet box order part no 193121A Adapter Assembly See Fig 1 The assembly includes an adapter ring two Screws and a cover plate to cover marks on the wall Install the ring and cover plate on the vertical outlet box For a wall installation hold the subbase in position and mark holes for the anchors See Fig 2 Obtain wall anchors locally T
12. lign the two captive mounting screws in the thermostat base with the posts on the subbase See Fig 14 Tighten both screws Do not overtighten screws or damage to subbase can result 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES L1 HOT 2 A oy r e Es CHANGEOVER RELAY FAN AUTO FAN RELAY ANTICIPATOR SEQ2 AUXILIARY HEAT 1 up A SEQ1 YELLOW 1 ue ee SWITCH EM HT RELAY 4R H2 LED ANTICIPATOR RED 4R SYSTEM LED GREEN HPS 4R Y POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED COMPRESSOR 4R CONTACTOR A REMOVE JUMPER FOR INDEPENDENT CONTROL OF W AND E TERMINALS M1627A Fig 11 Internal schematic and typical hookup for T874R Q674L in heat pump system Includes AUX HT CHECK and SYSTEM LEDs TOP WIRING THERMOSTAT FOR STRAIGHT MOUNTING TERMINAL CABLE OPENING INSERTION FOR WRAPAROUND SPIRIT LEVEL HOLES 2 STRIP 5 16 in 8 mm STRIP 7 16 in 11 mm BARRIER SUBBASE TERMINAL SCREW M928 Fig 13 Wiring connections MOUNTING POST 2 FOR LTO SPRING FINGER HOLES 2 MOUNTING CONTACTS ON THE THERMOSTAT THERMOSTAT UPTO12 woo Fig 12 Subbase components and leveling procedure 69 0268 11 10 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES
13. most systems the compressor has failed and the heat pump is not operating LEDs are not field replaceable or addable Copyright 1995 Honeywell Inc All Rights Reserved RECYCLING NOTICE This control contains mercury in a sealed tube Do not place the control in the trash at the end of its useful life If this control is replacing a control that contains mercury a sealed tube do your old control in the trash Contact your local waste management authority for instructions regarding recycling and the proper disposal of this control or of an old control containing mercury in a sealed tube INSTALLATION When Installing this Product 1 Read these instructions carefully Failure to follow them could damage the product or cause a hazardous condition 2 Check the ratings given in the instructions and the product to make sure the product is suitable for your application 3 Installer must be a trained experienced service technician 4 After installation is complete check out product operation as provided in these instructions 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES A CAUTION Disconnect power supply to prevent electrical shock or equipment damage 2 Run wires as close as possible to the subbase To prevent interference with the thermostat linkage keep wire length to a minimum Push excess wire back into the hole and plug the hole to prevent dra
14. r operation The proper thermistor operation must be verified to assure the correct operation of the thermostat Check thermistor operation as follows Disconnect the T wire on the subbase Use an ohmmeter to measure resistance between the T wire and the transformer secondary common or C terminal Take outdoor temperature at thermistor location and find the correct thermistor resistance on chart in Fig 15 If the resistance measured in step 2 and the calculated resistance in step 3 vary by more than 15 percent the thermistor requires replacement Contact the installation dealer for an outdoor thermistor replacement e o CALIBRATION Thermostat These thermostats are accurately calibrated at the factory They do not have provision for field calibration Thermometer The thermometer in your thermostat has been accurately calibrated at the factory The thermometer should only need adjustment if it has been dropped or jarred 69 0268 11 T874G R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F J L SUBBASES If the setpoint lever setting and the thermometer reading Insert a small screwdriver in the thermometer shaft do not agree follow the procedure below Fig 16 and turn it until the thermometers read the Remove thermostat cover by pulling the bottom same When the thermometer is calibrated replace edge of the cover outward and away from the base cover and place into operation until it clears the retaining posts S
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