X-XX UL
INSTALLATION INSTRUCTIONS
®U.S. Registered Trademark
Copyright © 1997 Honeywell Inc. • • All Rights Reserved
69-0774B-1
T874D Multistage Thermostat and
Q674A,D Subbases
APPLICATION
The T874D Thermostat and Q674A,D Subbases provide
24 to 30 Vac control of standard 2 stage heating and 2
stage cooling systems.
Q674A Subbase provides HEAT-AUTO-COOL system
switching and AUTO-ON fan switching.
OPERATION
The 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.
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
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 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.
IMPORTANT
An incorrectly leveled subbase will cause the
temperature control to deviate from setpoint. It is
not a calibration problem.
CAUTION
1.
Disconnect power supply to prevent electrical
shock or equipment damage.
2.
To prevent interference with the thermostat
linkage, keep wire length to a minimum and
run wires as close as possible to the subbase.
3.
Do not overtighten thermostat captive
mounting screws because damage to
subbase threads can result.
4.
Do not short across coil terminals on relay.
This can burn out the thermostat heat
anticipator.
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 may 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.
Mount 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 Honeywell part no. 193121A Adapter
Assembly. See Fig. 1. The assembly includes an
adapter ring, two screws and a cover plate to cover
marks on the wall. Install the ring and cover plate on
the vertical outlet box.
For a wall installation, hold subbase in position and mark
holes for anchors. See Fig. 2. Wall anchors must be
obtained from local hardware store. Be careful that the
wires do not fall back into the wall opening. Set aside
subbase. Drill four 3/16 in. (4.6 mm) holes and gently tap
anchors into the holes until flush with the wall.
2.
Pull electrical wires through the cover plate (if used)
and subbase cable opening. See Fig. 3.
3.
Secure the cover plate (if used) and subbase with
the screws provided. Do not fully tighten the
subbase screws.
