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Honeywell T874G Installation Instructions Manual

Multistage heat pump thermostats and subbases
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T874G,R Multistage Heat Pump Thermostats
APPLICATION
The T874G,R Thermostats with Q674F,J,L Subbases
provide 24 to 30 Vac control of a two-stage heating/one-
Thermostat/Subbase
T874G/Q674F
T874G/Q674J
T874R/Q674L
OPERATION
On a two-heat thermostat, the two stages of heat
sequentially as the temperature drops.
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
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
most systems, the compressor has failed and the heat
pump is not operating.
LEDs are not field replaceable or addable.
Copyright © 1995 Honeywell Inc. •
Table 1. Thermostat/Subbase Specifications.
System
OFF-EM.HT.-HEAT-AUTO-COOL
EM.HT.-AUTO-OFF
EM.HT.-HEAT-OFF-COOL
make
Make
refers to the
interstage differential
.
• All Rights Reserved
and Q674F,J,L Subbases
stage cooling heat pump system. See Table 1 for
thermostat/subbase specifications.
Switching
AUTO-ON
AUTO-ON
AUTO-ON
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 in a sealed tube, do
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 on
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.
X-XX UL
INSTALLATION INSTRUCTIONS
Fan
Changeover
Auto and Manual
Auto
Manual
not
place your old
69-0268-11

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  Summary of Contents for Honeywell T874G

  • Page 1 T874G,R Multistage Heat Pump Thermostats APPLICATION The T874G,R Thermostats with Q674F,J,L Subbases provide 24 to 30 Vac control of a two-stage heating/one- Thermostat/Subbase T874G/Q674F OFF-EM.HT.-HEAT-AUTO-COOL T874G/Q674J EM.HT.-AUTO-OFF T874R/Q674L EM.HT.-HEAT-OFF-COOL OPERATION On a two-heat thermostat, the two stages of heat sequentially as the temperature drops.
  • Page 2: Mounting The Subbase

    T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES CAUTION Disconnect power supply to prevent electrical shock or equipment damage. Run wires as close as possible to the subbase. To prevent interference with the thermostat linkage, keep wire length to a minimum.
  • Page 3 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT FALL H1 ANTICIPATOR ANTICIPATOR FALL RISE C1 ANTICIPATOR RISE Fig. 3. Internal schematic and typical hookup for T874G/Q674F in heat pump system. Includes AUX. HT. and EM. SUBBASE FAN SWITCH AUTO SYSTEM SWITCH EM. HT. HEAT EM. HT.
  • Page 4 RISE POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. 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 69-0268—11 SUBBASE...
  • Page 5 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT FALL H1/C1 ANTICIPATOR FALL H2 ANTICIPATOR RESET POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. FACTORY-INSTALLED JUMPER. Fig. 5. Internal schematic and typical hookup for T874R/Q674L in heat pump system with outdoor reset. Includes...
  • Page 6 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT FALL H1/C1 ANTICIPATOR FALL ANTICIPATOR RESET POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS. Fig. 6. Internal schematic and typical hookup for T874R/Q674L in heat pump system with outdoor reset. Includes...
  • Page 7 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT ANTICIPATOR C ANTICIPATOR FALL ANTICIPATOR FALL POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. REMOVE JUMPER WHEN W1 RELAY IS USED. FACTORY-INSTALLED JUMPER. Fig. 8. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes CHECK, EM. HT.
  • Page 8 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT H1/C1 ANTICIPATOR FALL ANTICIPATOR FALL POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. 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.
  • Page 9: Mounting The Thermostat

    T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES THERMOSTAT H1/C1 ANTICIPATOR FALL ANTICIPATOR FALL POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. TERMINAL LABELED C/X ON SOME MODELS. W3 TERMINAL AVAILABLE ON SOME MODELS ONLY. Fig. 10. Internal schematic and typical wiring diagram for T874R/Q674L in heat pump system. Includes EM. HT.
  • Page 10 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES FALL H1/C1 ANTICIPATOR FALL ANTICIPATOR POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. REMOVE JUMPER FOR INDEPENDENT CONTROL OF W AND E TERMINALS. Fig. 11. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes AUX. HT., CHECK...
  • Page 11: Temperature Setting

    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 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.
  • Page 12 T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES If the setpoint lever setting and the thermometer reading do not agree, follow the procedure below. Remove thermostat cover by pulling the bottom edge of the cover outward and away from the base until it clears the retaining posts.

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T874rQ674fQ674jQ674l