X-XX UL
INSTALLATION INSTRUCTIONS
Copyright © 1995 Honeywell Inc. • • All Rights Reserved
T874G,R Multistage Heat Pump Thermostats
and Q674F,J,L Subbases
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.
Switching
Thermostat/Subbase
System
Fan
Changeover
T874G/Q674F
OFF-EM.HT.-HEAT-AUTO-COOL
AUTO-ON
Auto and Manual
T874G/Q674J
EM.HT.-AUTO-OFF
AUTO-ON
Auto
T874R/Q674L
EM.HT.-HEAT-OFF-COOL
AUTO-ON
Manual
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
interstage 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
most systems, the compressor has failed and the heat
pump is not operating.
LEDs are not field replaceable or addable.
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
not place 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 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.
69-0268-11
