Honeywell T874C Manual

Honeywell
Application
'The T874C Thennostat provides low voltage (24 to 30 Vac}
control for 2-stage heating and |-stage cooling systems.
The Q674F Subbase provides wiring terminals, AUX.
HEAT-HEAT PUMP-2 STG. HEAT-OFF-COOL system
switching, and AUTO-ON fan switching for heat pump
systems.
Operation
On a 2-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 the second
stage makes only when the first stage cannot handie the
load. This is the interstage differential.
The light emitting diode (LED) indicators on the subbase
light when something happens within the system. An LED is
included on the subbase. When the LED lights, refer to this
list for the meaning:
AUX. HT.: Auxiliary heat is operating, which means the
weather is so cold that the heat pump alone cannot
handle the load.
CHECK: System needs to be checked. See Heating/Cool-
ing System Instructions for specific meaning.
LEDs are not field replaceable.
Recycling Notice
Installation Instructions for the Trained Service Technician.
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 op-
eration as provided in these instructions.
j CAO"
- 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 link-
age. keep wire length to a minimum. Push
excess wire back into the hole, and plug the hole
to prevent drafts from affecting the thermostat
operation.
3. Donotovertighten the thermostat captive mount-
i rews because damage to subbase threads
4. Do not short across coil terminals on the relay.
This can burn out the heat anticipator.
IMPORTANT: Thermostats are calibrated at the factory
by using subbases mounted at true level. Inaccurate
subbase leveling causes thermostat control deviation.
LOCATION
Install the thermostat about 5 ft (1.5m) above the floor in
a well-circulated area of average temperature.
Do not instali the thermostat where it can be affected by:
This control contains mercury in a sealed tube. Do nor
place control in the trash at the end of its useful life.
If this control is replacing a control that contains mercury
ina sealed tube, do nor place your old control in the trash.
Contact your local waste management authority for
insteuctions regarding recycling and the proper disposal of
this control, or of an old control contaiaing mercury in a
scaled tube.
If you have questions, call Honeyweil inc. at 1-800-
468-1502,
Installation
WHEN INSTALLING THIS PRODUCT...
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazardous
condition.
drafts, or dead spots behind doors and in comers.
— 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 AND WIRING THE SUBBASE
Disconnect the power supply to prevent electrical shock
or equipment damage. All wiring must comply with local
electrical codes and ordinances. Follow equipment manu-
facturer wiring instructions when available.
Mount the subbase on a wall or horizontal outlet bos. [Fit
is mounted on a vertical outlet box, order 193121A Adapter
Assembly, which includes adapter ring with two screws, and
a cover plate to cover marks on the wall,
To install subbase:
1. Prepare a hole for the thermostat wires at the chosen
location. Run the wires to the location.
2. Pull about 6 in. (152 mm) of wire through the hole.
JH. + Rev. 12-94 + (Q) © OHoneywell Inc. 1994 + Form Number 69-0851—I