Honeywell Thermostat T874/Q674 User's Manual
Contents
1. hold subbase in position and mark holes for anchors Fig 2 Obtain wall anchors locally Take care that the wires do not fall back into the wall opening Set aside subbase Drill four 3 16 in 4 8 mm holes and gently tap anchors into the holes until flush with the wall 2 Pull wires through the cover plate if used and subbase cable opening Fig 3 3 Secure the cover plate if used and subbase with the screws provided Do not fully tighten the subbase screws 4 Level the subbase using a spirit level as shown in Fig 3 and firmly tighten the subbase mounting screws The subbase mounting holes provide for minor out of level ad justments IMPORTANT An incorrectly leveled subbase will cause the temperature control to deviate from set point WIRING THE SUBBASE IMPORTANT Use 18 gauge color coded thermostat cable for proper wiring Disconnect power supply before beginning installation to prevent electrical shock or equipment damage All wiring must comply with local electrical codes and ordinances Follow equipment manufacturer wiring instruc tions when available To wire subbase proceed as follows 1 Connect the system wires to the subbase as shown in Figs 5 7 A letter code located near each terminal is for identification The terminal barrier permits straight or con ventional wraparound wiring connection Fig 4 2 Firmly tighten each terminal screw 3 Fit wires as close as possible to the subbase Push excess2. a minimum and run wires as close as possible to the subbase Push excess wire back into the hole and plug hole to prevent drafts from affecting thermostat opera tion 3 Donotovertighten thermostat captive mounting screws because damage to subbase threads may result 4 Do not short across coil terminals on the relay This may burn out the thermostat heat anticipator IMPORTANT Thermostats are calibrated at the factory using subbases mounted at true level An inaccurately leveled subbase will cause thermostat control devia tion S M Rev 5 93 C OHoneywell Inc 1993 Form Number 60 1147 4 LOCATION Install the thermostat about 5 ft 1 5 m above the floor in an area with good air circulation at average 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 1 If you must mount the subbase on a vertical outlet box order 193121A Adapter Assembly Fig 1 The as sembly includes an adapter ring two screws and acover plate to cover marks on the wall Install the ring and cover plate on the vertical outlet box For a wall installation
3. record the reading 4 After mounting the thermostat set the adjustable heat anticipator to match the reading measured in step 3 Fig 10 Stage two adjustable heat anticipator MOVE INDICATOR TO MATCH CURRENT RATING OF PRIMARY CONTROL M3684 60 1147 4 TEMPERATURE SETTING Fig 11 Location of external components T874N shown HEATING OPTIONAL LED j COOLING SET POINT ENUNCIATION SET POINT LEVER y LEVER SOT e 50 60 70 80 Spee THERMOMETER NN FAN SYSTEM WHEN PROVIDED SWITCH SWITCH M3525 The T874N has separate heating and cooling set point levers the T874R has one set point lever for heating and cooling Move the heating and cooling set point levers Fig 10 to the desired comfort positions The minimum differen tial between heating and cooling set point is 3 F 2 C on the T874N SUBBASE SETTING A description of the subbase switching positions that control the system operation follows Fig 11 SYSTEM SWITCH some subbases do not have all of the following functions OFF Both the heating and cooling systems are off If the fan switch is in AUTO position the cooling fan is also off AUTO Thermostat automatically changes between heat ing and cooling system operation depending on the indoor temperature HEAT Heating system is automatically controlled by the thermostat Cooling system is off COOL Cooling system is automatically
4. Honeywell T874 Q674 Thermostat Subbase Combinations Installation Instructions for the Trained Service Technician Application The T874 Q674 Thermostat Subbase combinations provide 24 to 30 Vac control for heat pump systems See Table 1 TABLE 1 T874 Q674 THERMOSTAT SUBBASE COMBINATIONS Thermostat Number Changeover Subbase of Stages Stage Type of Switching Model Heating Cooling Heating Cooling System Fan See Fig T874N Q674C 2 1 1 OFF AUTO AUTO ON 5 T874N Q674F 2 1 1 OFF EM HT AUTO ON 6 HEAT AUTO COOL T874R Q674L 2 1 a gt EM HT HEAT AUTO ON y OFF COOL Q674 Subbase provides the wiring terminals system switch and fan switch for system operation Provides manual changeover with the subbase system switch in COOL position Operation Installation 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 interstage differential One or two 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 ofthe system See your heating system instructions for the specific mean ing The EM H
5. T LED lights when the system switch is placed in the EM HT position Emergency heat is operating in most systems the compressor has failed and the heat pump is not operating The AUX HT LED lights when the auxiliary heat stage is operating The weather is cold enough that the first stage cannot handle the load alone LEDs are not field replaceable or addable Recycling Notice This control contains mercury in a sealed tube Do not place control in the trash at the end of its useful life If this control is replacing a control that contains mercury in a sealed tube do not place your old control in the trash Contact your local waste management authority for in structions regarding recycling and the proper disposal of this control or of an old control containing mercury in a sealed tube If you have questions call Honeywell at 1 800 468 1502 WHEN INSTALLING THIS PRODUCT 1 Read these instructions carefully Failure to follow them could cause a hazardous condition 2 Check the ratings given in the instructions and on the product to make sure the product is suitable for your applica tion 3 Installer must be a trained experienced service tech nician 4 After installation is complete check out product opera tion as provided in these instructions N CAUTION 1 Disconnect power supply to prevent electrical shock and equipment damage 2 Toprevent interference with the thermostat link age keep wire length to
6. Y CONTACT REVERSING VALVE HEAT RELAY 2 SYSTEM SWITCH co Ci ANTICIPATOR cooL t IND EM HEAT LED RED CHECK LED GREEN HIGH PRESSURE SWITCH OPTIONAL COMPRESSOR FAILURE DEVICE COMPRESSOR CONTACTOR A POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED 60 1147 4 M3686 Fig 7 Internal schematic and typical wiring diagram for T874R and Q674L EM HT RELAY CONTACT EM HT RELAY HEAT CONTACT CONTACTOR 3 E H1 C1 O ANTICIPATOR OUTDOOR HEAT THERMOSTAT CONTACTOR 2 DEFROST wee HEAT HIGH LIMIT O l EL RELAY 1 SWITCH Hi Ct DEFROST REVERSING Lo RELAY VALVE O Ear He FAN SWITCH O AUTO AUX HEAT i LED GREEN QS on CHA SN AN 9 ANTICIPATOR FALL x3 4 d SYSTEM Baier SWITCH EM HEAT i LED RED RELAY O EM HT FL A o FAN RELAY HEAT Q OFF i ata X oH LOW COMPRESSOR HIGH AMBIENT CONTACTOR PRESSURE COOL C Ww B AMBIENT EU POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED Ev COOL RELAY HoH M3685 4 Turn over thermostat base and note the spring fingers that engage the subbase contacts Make sure the spring fingers are not bent flat Flat fingers prevent proper electrical contact with the subbase 5 Set the second stag
7. controlled by the thermostat Heating system is off EM HT Emergency heat relay is automatically con trolled by the thermostat Cooling system is off FAN SWITCH ON Fan operates continuously AUTO Fan operates automatically with heating and cooling equipment as controlled by the thermostat To move the subbase switches to the desired control positions use thumb and index finger to slide lever Lever must stop over desired function indicator position for proper circuit operation Checkout HEATING Move the system switch on the Q674 to HEAT or AUTO if used and the fan switch to AUTO Move the heating set point lever on the T874 about 10 F 6 C above room temperature Heating equipment should start and the fan should run Move the heat lever about 10 F 6 C below room temperature The heating equipment and fan should shut off NOTE In heat pump applications time delays are involved before the compressor is activated to prevent short cy cling The delays are provided by a timer which prevents the compressor from starting for several minutes after the thermostat last turned the compressor off or after the system first received power COOLING Move the system switch on the Q674 to COOL or AUTO if used and the fan switch to AUTO Move the cooling set point lever on the T874 about 10 F 6 C below room temperature The cooling equipment should start see NOTE above Move the cool lever about 10 F 6 C ab
8. e index finger to gently pull out the plastic set point scale about 1 4 in 6 mm Drop insert into recessed area behind set point scale so that selected LEDs show Make sure insert is com pletely seated in recessed area Let set point scale pop back and set levers to desired positions Fig 4 Wiring connections FOR STRAIGHT INSERTION STRIP 5 16 in 8 mm FOR WRAPAROUND STRIP 7 16 in 11 mm SUBBASE TERMINAL SCREW M928 Fig 5 Internal schematic and typical wiring diagram for T874N and Q674C Hi DEFROST RELAY CONTACT L1 L2 HOT A eT OUTDOOR THERMOSTAT REVERSING RELAY HEAT RELAY 2 ENS ANTICIPATOR O FALL FAN SGH EM HT RELAY HEAT CONTACT RELAY 3 Hi EN AUTO A 1 VJ 9 FALL ON LA FAN RELAY ee O H2 ANTICIPATOR O eH HEAT RELAY 1 SYSTEM A SWITCH lan Pt NU 1 WH OFF CHECK Ci cp LED ANTICIPATOR AUTO GRN OPTIONAL OY O c1 F co RISE Da o O Q A POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED COMPRESSOR CONTACTOR M1860 60 1147 4 Fig 6 Internal schematic and typical wiring diagram for T874N and Q674F O Hi ANTICIPATOR O ANTICIPATOR FAN SWITCH 9 Far OUTDOOR THERMOSTAT DEFROST RELAY EM HT RELAY CONTACT EM HT RELA
9. e heat anticipation indicator to match the current rating of the controlled equipment See Heat Anticipator Setting section The first stage heat antici pator and the cooling anticipator are nonadjustable 6 Note the two tabs on the top inside edge of the thermostat base The tabs fit into corresponding slots on top of the subbase Mount the thermostat on the subbase 7 Align the two captive mounting screws in the thermo stat base with the posts on the subbase Fig 9 Tighten both screws Do not overtighten screws because damage to subbase posts can result Fig 8 LED space location and adjustable lever stops LED SPACE TIGHTENING SCREW ADJUSTABLE STOPS 60 1147 4 Fig 9 Mounting thermostat on subbase THERMOSTAT MOUNTING SLOTS 2 THERMOSTAT MOUNTING POST 2 CAPTIVE MOUNTING Ma36 SCREWS 2 Settings HEAT ANTICIPATOR SETTING Set the adjustable heat anticipator to match the current draw ofthe second stage heating primary control Fig 10 If the primary control nameplate has no rating or if further adjustment is necessary use the following procedure to determine the current draw of the second stage NOTE The current draw ofthe heating stage must be measured with the thermostat removed and the power on 1 Connect an ac ammeter of appropriate range between the W2 and R terminals on the subbase 2 Move the system switch to HEAT or AUTO 3 After one minute read the ammeter and
10. ove room temperature The cooling equipment and fan should shut off FAN Move the subbase system switch to OFF and the fan switch to ON The fan should run continuously Move the fan switch to AUTO In this position fan operation is controlled by the heating or cooling system control circuit Calibration THERMOSTAT T874 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 need adjustment only if it has been dropped or shifted due to mishandling If the set point lever and the thermometer reading do not agree 1 Remove the thermostat cover by pulling up from the bottom of cover until it clears the mounting slots 2 Set the thermostat cover on a table near an accurate thermometer 3 Allow 10 or 15 minutes for cover thermometer to sense area temperature compare the readings Be careful not to touch the thermometer or breathe on it 4 Ifthe readings are the same replace the cover and put the system into operation 5 If the readings are different insert a small screw driver in the thermometer slot Fig 12 and turn it until the thermometers have the same reading 6 Replace thermostat cover and put the system into operation NOTE Radiant heat from your hands will offset the ther mometer reading After making each adjustment wait 10 or 15 minutes fo
11. r the thermometer to stabilize before comparing Fig 12 Thermometer calibration tan M5070 60 1147 4 Honeywell Automation and Control Solutions Honeywell International Inc 1985 Douglas Drive North Golden Valley MN 55422 60 1147 4 S M Rev 5 93 Honeywell Limited Honeywell Limit e 35 Dynamic Drive Scarborough Ontario M1V 4Z9 Printed in U S A on recycled paper containing at least 10 post consumer paper fibers www honeywell com yourhome
12. wire back into the hole 4 Plug hole with nonflammable insulation to prevent drafts from affecting the thermostat MOUNTING THE THERMOSTAT 1 Remove the thermostat cover by pulling the bottom edge of the cover outward and away from the base until it snaps free of the mounting slots NOTE The coveris hingedatthe top and must be re moved by pulling outward at the bottom 60 1147 4 Fig 1 Installation of Q674 Subbase on outlet box ADAPTER S RING y A MOUNTING y SCREWS 2 SCREWS 2 MOUNTING SUBBASE SCREWS 2 Anor INCLUDED WITH UNIT A accessory PARTS AVAILABLE 193121A M925 Fig 2 Installation of Q674 Subbase on wall WIRES THROUGH WALL OPENING E HOLES XN SUBBASE b IOUNTING M926 SCREWS 2 Fig 3 Subbase componenis and leveling procedure TOP MOUNTING HOLES 2 WIRING TERMINAL THERMOSTAT SPIRIT LEVEL CABLE OPENING O uj S Da to ca va Do C9 t uj ba zl ca Ca IOUNTING HOLES 2 POST 2 FOR TO SPRING FINGER CONTACTS MOUNTING ON THE THERMOSTAT THERMOSTAT UP TO 12 M927 2 Carefully remove and discard the polystyrene packing insert that protects the mercury switches during shipment 3 If LED indication EM HT CHECK etc is to be used with the Q674 Subbase install the preprinted insert under the thermostat set point scale Fig 8 To install push both thermostat set point levers to the far ends of the thermostat Us
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