Honeywell T874 Quick Start Manual page 2

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.
4. Level the subbase using a spirit level, see Fig. 3, and
firmly tighten subbase mounting screws. The subbase mount-
ing 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.
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 instruc-
tions 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
Fig. 5—Schematic and hookup for T874D Thermostat with Q674E Subbase.
FALL
H1
FALL
H2
RISE
C1
RISE
C2
WALL
MOUNTING
HOLES
MOUNTING
SCREWS (2)
H1 ANTICIPATOR
H2 ANTICIPATOR
FAN
SWITCH
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.
Fig. 3—Subbase components and leveling
procedure.
SPIRIT LEVEL
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
AUTO
ON
SYSTEM
SWITCH
OFF
HEAT
AUTO
COOL
2
TOP MOUNTING HOLES (2)
WIRING
TERMINAL
THERMOSTAT
CABLE OPENING
MOUNTING HOLES (2)
POST (2) FOR
MOUNTING
THERMOSTAT
FOR WRAPAROUND–
STRIP 7/16 in. [11 mm]
BARRIER
W1
HEAT RELAY 1
W2
HEAT RELAY 2
B
CHANGEOVER
RELAY (HEAT)
RH
2
RC
O
CHANGEOVER
RELAY (COOL)
G
FAN RELAY
Y2
COMPRESSOR
CONTACTOR 2
Y1
COMPRESSOR
CONTACTOR 1
M927
M928
1
L2
L1
(HOT)
L1
(HOT)
L2
1
M3203