Honeywell T874A Installation Instructions Manual

APPLICATION
These thermostat/subbase combinations provide low voltage (24 Vac) control in multistage systems as follows:
Number of
Stages
Thermostat/
Subbase
Heat
T874A/Q674Q 1
T874D/Q674F 2
T874R/Q674B 2
T874D/Q674D 2
T874D/Q674B 2
OPERATION
On a two-stage 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 called the interstage differential .
The LED indicators are light emitting diodes on the
subbase that light up when something specific happens
within the system. When an LED lights up, refer to this list
for the meaning:
AUX. HEAT: Auxiliary heat is operating, which means
the weather is so cold that the heat pump alone
cannot handle the load.
HEAT PUMP: System needs to be checked. See
heating system instructions for specific meaning.
LEDs are not field replaceable.
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.
®U.S. Registered Trademark
Copyright © 1996 Honeywell Inc. • All Rights Reserved
T874A,D,R Thermostats and
Cool
1 HEAT-OFF-COOL
2 AUX HT-HEAT PUMP-2 STG. HEAT-OFF-COOL
1 HEAT-OFF-COOL
2
2 HEAT-OFF-COOL
Q674B,D,F,Q Subbases
INSTALLATION INSTRUCTIONS
Switching Positions
System
None
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 hazard-
ous 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
Wiring
Fig.
Fan
LO-MED-HIGH-ON
AUTO-ON
AUTO-ON 6,7
None
AUTO-ON
69-0107-2
4
5
8
9