!
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
TEMPERATURE LEVER STOPS
!
The T874D has factory-installed temperature lever locking screws and stop brackets. See Figs. 6 and 7. These
should be used only if the HEAT and COOL temperature
setpoint lever ranges are to be restricted.
Fig. 6—Location of locking lever screws.
LEVER LOCKING SCREWS
M18680
Fig. 8—Installing locking lever screws and stop
brackets.
HOLES FOR INSULATED
LOCKING LEVER SCREWS
HEAT
LEVER
COOL
LEVER
HOLE WITH
BRASS INSERT
BRACKET
TABS
Fig. 7—Location of lever stop brackets.
LEVER STOP BRACKETS
M18681
INSTALL AND ADJUST LOCKING LEVER
SCREWS
The two screws with insulated heads should be used
only if the HEAT and COOL levers are to be locked in
place at a specific temperature control point. Do not use
standard screws that provide metal-to-metal contact with
the lever brackets.
To install:
1. Refer to Fig. 8 for screw hole locations.
2. Install the two screws with insulated heads in the
indicated holes Do not overtighten screws.
3. Set the HEAT lever and the COOL lever at desired
temperature control points.
4. Firmly tighten both screws.
INSTALL AND ADJUST STOP BRACKETS
The stop brackets should be installed only if there is a
need to restrict the adjustable range of the heating and
cooling temperature setpoint levers. See Fig. 6.
To install:
1. Turn over the T874 Thermostat to the back side.
Locate the hole in the plastic base for the brass insert. See
Fig. 9.
2. Push brass insert into the hole with your finger.
3. Turn to front side of the T874 Thermostat.
4. Place the two stop brackets in position with the tabs
in the slot between the HEAT and COOL levers. See Fig. 8.
5. Insert the mounting screws into the two slots in the
stop brackets and attach to the brass insert. Tighten the
screw to pull the brass insert into the back of the thermostat.
6. Loosen the mounting screw enough to slide the stop
brackets for adjustment.
7. Move the HEAT and COOL setpoint levers to the
maximum temperature that is desired.
8. Slide the stop brackets until one rests against the
HEAT lever and the other against the COOL lever.
ADJUSTABLE
LEVER STOP
BRACKETS
BRACKET
SLOTS
MOUNTING
SCREW
M7346
Fig. 9—Installing brass insert.
LED WINDOW
BRASS INSERT
INSERT HOLE
BACK OF
THERMOSTAT
M955A
9. Firmly tighten the mounting screw.
10. If the HEAT and COOL levers are to be locked in
place at a specific temperature, use the two insulated head
screws supplied instead of the two adjustable lever stop
brackets.
CAUTION
Do not use standard screws that provide metal-tometal contact with the stop brackets. Short circuit and potential equipment damage may result.
3 69-0753
MOUNT THERMOSTAT
)
1. Remove the thermostat cover by pulling the bottom
edge of the cover upward until it snaps free of the mounting slots.
NOTE: The cover is hinged at the top and must be removed
by pulling up at the bottom.
2. Carefully remove and discard the polystyrene packing
insert that protects the mercury switches during shipment.
3. Turn over thermostat base and note the spring fingers
that engage the subbase contacts. Make sure the spring
fingers are not bent flat, preventing proper electrical contact with the subbase.
4. Note the two tabs on the top inside edge of the
thermostat base. The tabs fit into corresponding slots on top
of the subbase. Mount the thermostat on the subbase.
5. Align the two captive mounting screws in the thermostat base with the posts on the subbase. See Fig. 10.
Tighten both screws. Do not overtighten screws or damage
to subbase posts can result.
Fig. 10—Mounting thermostat on subbase.
THERMOSTAT
MOUNTING SLOTS (2)
THERMOSTAT
MOUNTING POST (2)
COOL
50 60 70 80
50 60 70 80
SUBBASE
THERMOSTAT
M936
HEAT
CAPTIVE MOUNTING
SCREWS (2
Settings
SET THE HEAT ANTICIPATOR
Move the indicator to match the current rating of the
primary control. See Fig. 11. When using the T874 Thermostat with two stages of heating, set each heat anticipator to match its respective primary control current draw. If
you cannot find the current rating on the primary control,
or if further adjustment is necessary, see NOTE below and
use the following procedure to determine the current draw
of each stage.
The current draw of each heating stage must be measured with the thermostat removed and the power on to the
heating system.
1. Connect an ac ammeter of appropriate range between
the heating terminals of the subbase:
Stage 1—between W1 and RH;
Stage 2—between W2 and RH.
2. Move the system switch to HEAT or AUTO.
3. After one minute, read the ammeter and record the
reading:
Stage 1—__________ amperes.
Stage 2—__________ amperes.
4. After mounting the thermostat, set the adjustable
heat anticipator to match the readings measured in Step 3.
NOTE: If equipment cycles too fast, set the indicator to a
higher current rating, not more than one-half division at
a time, and recheck cycle rate. Most conventional two-
stage heating equipment is designed to operate at three
cycles per hour per stage and one-stage heating equip-
ment at six cycles per hour, at 50 percent load condition.
TEMPERATURE SETTING
Move the heating and cooling setpoint levers to the
desired comfort positions. See Fig. 12. One lever controls
all stages of heating, and the other lever controls all stages
of cooling. The minimum differential between heating and
cooling setpoint is 3° F [1.7° C], which means the setting
levers are designed so they cannot be set closer together
than 3° F [1.7° C].
INSTALL OR REMOVE TG504A KEY LOCK
COVER
To install the TG504A:
—hang the upper edge of the cover on the thermostat
subbase.
—swing cover downward.
Spring-loaded locking mechanism will automatically
engage mounting posts and secure cover in final position
without use of key provided.
To remove the TG504A:
— insert the key provided.
— rotate the key clockwise until locking mechanism
releases from thermostat posts.
— swing cover upward and off.
Fig. 11—Adjustable heat anticipator scales.
.12
.15
.2
.3
.4
.5
.6
.8
1.2
.10
.12
.15
.2
.3
.4
1.2
.8
.6
STAGE TWO
ANTICIPATOR
HEATING CONTROL
MOVE INDICATOR TO
MATCH CURRENT RATING
OF PRIMARY CONTROL
4
STAGE ONE
ANTICIPATOR
HEATING CONTROL
M5069
Fig. 12—Location of external components.
!
HEATING SET
POINT LEVER
HEAT
M3459
50 60
70 80
.3
.4
.6
1.2
.8
FAN
COOLING SET
POINT LEVER
HEAT
.12
1.5
.2
.3
.4
.6
.8
1.2
1.5
.2
ON
AUTO
FAN
SWITCH
50 60
70 80
AUTO
HEAT
COOL
OFF
SYSTEM
SWITCH
SUBBASE SETTING
The subbase switching positions control the system
operation as follows (see Fig. 12):
SYSTEM SWITCH (some subbase do not have all of the
following functions):
OFF—both the heating and cooling systems are off. If
the fan switch is in AUTO position, the cooling fan is
also off.
HEAT—heating system is automatically controlled by
the thermostat. Cooling system is off.
AUTO—thermostat automatically changes between
heating and cooling system operation, depending on
the indoor temperature.
COOL—cooling system is automatically controlled by
the thermostat. Heating system is off.
FAN SWITCH
ON—fan operates continuously.
AUTO—fan operates with cooling equipment as con-
trolled by the thermostat or with the heating equip-
ment as controlled by the plenum switch.
To move the subbase switches to the desired control
positions, use thumb and index finger to slide lever. Lever
must stop over desired function indicator position for
proper circuit operation.
Checkout
HEATING
Move the system switch on the Q674 to HEAT or
AUTO, and the fan switch to AUTO. Move the heating
setpoint lever on the T874 about 10° F [6° C] above room
temperature. Heating equipment should start and the fan
should run. Move the heating lever about 10° F [6° C]
below room temperature. The heating equipment and fan
should shut off.
NOTE: In heat pump applications, a minimum off-timer
provides a five-minute time delay before starting compressor when the thermostat last turned off the compressor, or when the system first received power. This delay
prevents compressor short cycling.
COOLING
CAUTION
If outside air or heat exchange medium (water) is
below 50° F [10° C], do not operate cooling.
Move the system switch on the Q674 to COOL or AUTO,
and the fan switch to AUTO. Move the cooling setpoint
lever on the T874 about 10° F [6° C] below room tempera-
ture. The cooling equipment should start (see Note). Move
the cool lever about 10° F [6° C] above room temperature.
The cooling equipment and fan should shut off.
NOTE: If using a Control Module Mark IV, there are
time delays built-in. Check your Mark IV instructions
for specifics.
FAN
Move the subbase system switch to OFF, and the fan
switch to ON. The fan should run continuously. Move the
fan switch to AUTO. In this position, fan operation is
controlled by the heating or cooling system control circuit.
INSTALL OR REMOVE TG504A KEY LOCK
COVER
To install the TG504A:
—hang the upper edge of the cover on the thermostat
subbase.
—swing cover downward.
Spring-loaded locking mechanism will automatically
engage mounting posts and secure cover in final position
without use of key provided.
To remove the TG504A:
— insert the key provided.
— rotate the key clockwise until locking mechanism
releases from thermostat posts.
— swing cover upward and off.
Calibration
THERMOSTAT
T874 Thermostats are accurately calibrated at the fac-
tory. They do not have provision for field calibration.
5 69-0753
Home and Building Control Home and Building Control Helping You Control Your World
Honeywell Inc. Honeywell Limited—Honeywell Limitée
1985 Douglas Drive North 740 Ellesmere Road
Golden Valley, MN 55422 Scarborough, Ontario
M1P 2V9
Printed in U.S.A. www.honeywell.com/yourhome
6
QUALITY IS KEY
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