Honeywell Q674E, Q674D, Q674B, T874A, T874D User Manual
T874A,D Zone T hermostats/
Q674B,D,E Subbases
Installation Instructions for the Trained Service Technician.
Application
These T874A,D Zone Thermostats and Q674B,D,E
Subbases provide 24 to 30 Vac temperature control in
Honeywell Trol-A-Temp heating/cooling zone systems.
TABLE 1—THERMOSTAT/SUBBASE AND SYSTEM COMPATIBILITY.
Thermostat/ Application
Subbase Model
T874A/Q674B Zone 1; conventional Zone 1; conventional Any zone; conventional heat-cool. Single-stage
T874A/Q674D Zones other than zone 1; Zones other than zone 1; Not applicable Single-stage
T874A/Q674E Not applicable Not applicable Any zone; conventional heat-cool. Single-stage
T874D/Q674B Not applicable Zone 1; conventional Any zone; conventional heat-cool. Multistage
T874D/Q674D Not applicable Zones other than zone 1; Not applicable Multistage
T874D/Q674E Not applicable Not applicable Any zone; conventional heat-cool. Multistage
a
Subbase not included with thermostat; order separately.
T874A1465/Q674B1471 HEAT-OFF-COOL ON-AUTO White/Gray Stg. 1— Stg. 1—
T874A1465/Q674D1123 None None White/Gray 0.1 to 1.2 0 to 1.5
T874A1465/Q674E1379 HEAT-OFF-COOL-AUTO ON-AUTO White/Gray
T874D1801/Q674B1463 HEAT-OFF-COOL ON-AUTO Beige/Brown Stg. 1— Stg. 1—
T874D1827/Q674B1471 HEAT-OFF-COOL ON-AUTO White/Gray 0.1 to 1.2; 0 to 1.2;
T874D1801/Q674D1115 None None Beige/Brown Stg. 2— Stg. 2—
T874D1827/Q674D1123 None None White/Gray 0.1 to 1.0. 0 to 1.0.
T874D1827/Q674E1379 HEAT-OFF-COOL-AUTO ON-AUTO White/Gray
a
Subbase not included with thermostat; order separately.
a
Number
Thermostat/Subbase Switching Subbase Heating Cooling
Order Number
Mini-Zone Mabs II, Mabs II-L Mabs XX Stages
heat-cool. heat-cool.
conventional heat-cool. conventional heat-cool.
heat-cool.
conventional heat-cool
and heat pump.
TABLE 2—THERMOSTAT/SUBBASE SPECIFICATIONS.
a
System Fan Color (Adj.) (Fixed)
See Table 1 for thermostat/subbase and system compatibility; see Table 2 for thermostat specifications. For complete
Honeywell Trol-A-Temp System specification and application information, refer to the system specification included with the control panel.
Thermostat/ Anticipator Range (A)
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 that the
second stage makes only when the first stage cannot
handle the load. This is the interstage differential.
S. M. • Rev. 6-93 • • ©Honeywell Inc. 1993 • Form Number 69-0580—2
Recycling Notice
M3375
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.
If you have questions, call Honeywell at 1-800-468-1502.
M3375
Installation
M3703
SUBBASE
HORIZONTAL
OUTLET
BOX
1
NOT INCLUDED WITH UNIT.
1
WHEN INSTALLING THIS PRODUCT…
1. Read these instructions carefully. Failure to follow them could damage the product or 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 terminals of systems controls. This can burn out the thermostat heat
anticipator.
IMPORTANT: Thermostats are calibrated at the factory by
using subbases mounted at true level. Inaccurate subbase leveling will cause thermostat control deviation.
LOCATION
Locate the subbase about 5 ft [1.5 m] above the floor in
an area with good air circulation at average temperature.
Do not mount the subbase where the thermostat may be
affected by:
— drafts or dead spots behind doors and in corners.
— hot or cold air from ducts.
— radiant heat from sun, appliances or fireplace.
— concealed pipes and chimneys.
— unheated (uncooled) areas such as an outside wall
behind the thermostat.
MOUNTING THE SUBBASE
The thermostat subbase can be mounted on a horizontal
outlet box or directly on the wall.
1. To mount on a horizontal outlet box, install the sub-
base on the outlet box as shown in Fig. 1.
For a wall installation, hold the subbase in position and
mark holes for the anchors (Fig. 2). Obtain wall anchors
locally. Take care that the wires do not fall back into the
wall opening. Set aside subbase. Drill two 3/16 in. [4.8 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 (Fig. 3). See Wiring the Subbase section before pulling any wires.
IMPORTANT: Use 18 gauge, color-coded thermostat
cable for proper wiring.
3. Secure the subbase with the screws provided. Do not
fully tighten the subbase screws.
Fig. 1—Installation of subbase on outlet box.
Fig. 2—Installation of subbase on wall.
WALL
WIRES THROUGH
WALL OPENING
WALL
ANCHORS
(2)
M926
Fig. 3—Subbase components and leveling
procedure.
SPIRIT LEVEL
MOUNTING
HOLES (2)
TOP
MOUNTING
HOLES (2)
SUBBASE
WIRING
TERMINAL
POST (2) FOR
MOUNTING
THERMOSTAT
MOUNTING
HOLES
MOUNTING
SCREWS (2)
THERMOSTAT
CABLE OPENING
TO SPRING FINGER
CONTACTS ON THE
THERMOSTAT
(UP TO 12)
M927
4. Level the subbase using a spirit level, as shown in
Fig. 3, and firmly tighten the subbase mounting screws.
The subbase mounting holes allow minor out-of-level
adjustments.
IMPORTANT: An incorrectly leveled subbase will cause
the temperature control to deviate from set point.
WIRING THE SUBBASE
All wiring must comply with local electrical codes and
ordinances. Follow equipment manufacturer wiring instructions when available. To wire subbase:
1. Connect wires to the subbase terminals. Refer to
Figs. 6-10 for wiring diagrams of typical zone systems. A
2
letter code is located near each subbase terminal for identification. The terminal barrier permits straight or conventional wraparound wiring connection (Fig. 4).
2. Some Q674 Subbases have RC and RH terminals
for isolated heating and cooling transformers. For zoning
systems, jumper RC and RH terminals as shown in Fig. 5
and wire as single R terminal.
3. Firmly tighten each terminal screw.
4. Fit wires as close as possible to the subbase. Push
excess wire back into hole.
5. Plug the hole with nonflammable insulation to prevent drafts from affecting the thermostat.
Fig. 4—Wiring connections.
FOR STRAIGHT
INSERTION–
STRIP 5/16 in. [8 mm]
FOR WRAPAROUND–
STRIP 7/16 in. [11 mm]
Fig. 5—Jumper RC and RH terminals for single
transformer system. Strip wire 3/4 in. [19 mm].
RCR
H
W2
ZONE 1
RELAY
4
Y2
ZONE 2
RELAY
ZONE 2ZONE 1
M6
M4
T6
T5
T4
M1
RCR
H
T874A THERMOSTAT/
Q674D SUBBASE
4
3
Y1 Y2
RC
4 56Z
DAMPER
ACTUATOR
123X
RH W2
M1633
M929
W1
SUBBASE TERMINAL SCREW
Fig. 6—Typical hookup for MM-2 Mini-zone Control Panel with T874A Thermostat/Q674B,D Subbase in
single-stage heating-cooling two-zone system.
BARRIER
MINIZONE
(MM-2)
CONTROL
PANEL
Y2
Y1
O
TO SINGLESTAGE
HEATING/
COOLING
EQUIPMENT
G2
G1
RC
RH
B
W2
W1
E
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
1
ZONE 1 O AND B TERMINALS MUST BE CONNECTED FOR PROPER SYSTEM OPERATION.
2
JUMPER RC AND RH TERMINALS TOGETHER AND WIRE AS SINGLE R TERMINAL.
3
DO NOT CONNECT W2 AND Y2 TERMINALS TO CONTROL PANEL.
4
TRANSFORMER
L2
1
L1
(HOT)
M928
T874A THERMOSTAT/Q674B SUBBASE
2
OG B
HEAT
COOL
RELAY
RELAY
CHANGEOVER
CONTROL
O1
COOL
G1
FAN
B1
HEAT
B
2
24 V, 40 VA
1
3
RC RH W1
Y1
T6
T5
T4
M6
M4
M1
4 56Z
DAMPER
ACTUATOR
123X
3 69-0580—2
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