Honeywell T874D, Q674E User Manual
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SUPER TRADELINE
Thermostat and Q674 Subbase
T874 Multistage
Application
The T874D Thermostat and Q674E Subbase provide 24
to 30 Vac control of standard 2 stage heating and 2 stage
cooling systems.
The Y594D includes the TG504 Thermostat Guard,
field-adjustable range stops and field-adjustable locking
levers.
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.
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.
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.
Do not install 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 behind the thermostat,
such as an outside wall.
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 conceal any holes or blemishes
on the wall. Install the ring and cover plate on the vertical
outlet box.
Fig. 1—Installation of Q674 Subbase on outlet
box.
VERTICAL
OUTLET
1
BOX
ADAPTER
RING
MOUNTING
SCREWS (2)
SUBBASE
HORIZONTAL
OUTLET
BOX
1
SUBBASE
1 NOT INCLUDED WITH UNIT.
2 ACCESSORY PARTS AVAILABLE (193121A).
MOUNTING
SCREWS (2)
COVER
PLATE
2
2
MOUNTING
SCREWS (2)
M925
IMPORTANT: An incorrectly leveled subbase will cause
the temperature control to deviate from setpoint. It is
not a calibration problem.
LOCATION
Install the thermostat about 5 ft [1.5 m] above the floor
in an area with good air circulation at average temperature.
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.
1 69-0753J. H. • 11-92 • ©Honeywell Inc. 1992 • Form Number 69-0753
2. Pull electrical wires through the cover plate (if
(2)
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.
4. Level the subbase using a spirit level, see Fig. 3, and
firmly tighten subbase mounting screws. The subbase mounting holes provide for minor out-of-level adjustments.
IMPORTANT: An incorrectly leveled subbase will cause
the temperature control to deviate from setpoint. It is
not a calibration problem.
Fig. 2—Installation of Q674 Subbase on wall.
Fig. 3—Subbase components and leveling
procedure.
SPIRIT LEVEL
TOP MOUNTING HOLES (2)
WIRING
TERMINAL
THERMOSTAT
CABLE OPENING
WALL
WIRES THROUGH
WALL OPENING
WALL
ANCHORS
(2)
SUBBASE
M926
WIRING THE SUBBASE
All wiring must comply with local electrical codes and
ordinances. Follow equipment manufacturer wiring instructions when available. To wire subbase, proceed as follows:
1. Connect the system wires to the subbase as shown in
Figs. 5 through 8. A letter code is located near each terminal
MOUNTING
HOLES
MOUNTING
SCREWS
TO SPRING FINGER CONTACTS
ON THE THERMOSTAT
(UP TO 12)
for identification. The terminal barrier permits straight or
conventional wraparound wiring connection. See Fig. 4.
2. Firmly tighten each terminal screw.
3. Fit wires as close as possible to the subbase. Push
excess wire back into hole.
4. Plug hole with nonflammable insulation to prevent
drafts from affecting the thermostat.
Fig. 4—Barrier configuration.
FOR STRAIGHT
INSERTION–
STRIP 5/16 in. [8 mm]
SUBBASE TERMINAL SCREW
Fig. 5—Schematic and hookup for T874D Thermostat with Q674E Subbase.
FALL
H2
RISE
C2
FALL
H1
RISE
C1
H1 ANTICIPATOR
H2 ANTICIPATOR
FAN
SWITCH
AUTO
ON
SYSTEM
SWITCH
OFF
C1 ANTICIPATOR
C2 ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
2
JUMPER RC AND RH FOR A SINGLE TRANSFORMER SYSTEM.
HEAT
AUTO
COOL
MOUNTING HOLES (2)
BARRIER
W1
HEAT RELAY 1
W2
HEAT RELAY 2
B
CHANGEOVER
RELAY (HEAT)
RH
RC
O
CHANGEOVER
RELAY (COOL)
G
FAN RELAY
Y2
COMPRESSOR
CONTACTOR 2
Y1
COMPRESSOR
CONTACTOR 1
POST (2) FOR
MOUNTING
THERMOSTAT
FOR WRAPAROUND–
STRIP 7/16 in. [11 mm]
2
M927
M928
1
1
L2
L1
(HOT)
L1
(HOT)
L2
M3203
2
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