Honeywell Q674A E Thermostat User Manual

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TRADELINE  
T874A-F Multistage  
Thermostats/Q674A-E,G Subbases  
Installation Instructions for the Trained Service Technician.  
Application  
Installation  
The T874A-F Thermostats provide 24 to 30 Vac control  
for heating and/or cooling systems as listed in Table 1.  
WHEN INSTALLING THIS PRODUCT…  
1. Read these instructions carefully. Failure to follow  
them could damage the product or cause a hazardous condi-  
tion.  
2. Check the ratings given in the instructions and on the  
product to make sure the product is suitable for your  
application.  
TABLE 1—THERMOSTAT HEATING AND/OR  
COOLING STAGES.  
T874  
A
1
B
1
C
2
D
2
E
2
F
Heating Stages  
Cooling Stages  
2
3. Installer must be a trained, experienced service tech-  
nician.  
1
2
1
2
4. After installation is complete, check out product  
operation as provided in these instructions.  
The Q674A-E,G Subbases provide wiring terminals,  
system and fan switching, and mounting bases for T874  
Thermostats as listed in Table 2.  
CAUTION  
1
. Disconnect power supply to prevent electrical  
shock or equipment damage.  
TABLE 2—SUBBASE SWITCHING POSITIONS.  
Q674  
Switch Positions  
System  
2. To prevent interference with the thermostat  
linkage, keep wire length to a minimum and  
run wires close as possible to the subbase.  
Model  
Fan  
A
B
C
D
E
Heat-Auto-Cool  
Heat-Off-Cool  
Off-Auto  
Auto-On  
Auto-On  
Auto-On  
None  
3
. Do not overtighten thermostat captive mount-  
ing screws because damage to subbase threads  
can result.  
4
. Do not short across coil terminals on heating  
relay or gas control. This can burn out the  
thermostat heat anticipator.  
None  
Off-Heat-Auto-Cool  
Off-Auto  
Auto-On  
None  
G
IMPORTANT: Thermostats are calibrated at the factory  
by using subbases mounted at true level. Inaccurate  
subbase leveling will cause thermostat control de-  
viation.  
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.  
LOCATION  
Locate the subbase about 5 ft [1.5m] 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.  
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 mer-  
cury 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.  
MOUNTING THE 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 193121A Adapter Assembly (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.  
J.H. • Rev. 5-94 •
• ©Honeywell Inc. 1994 • Form Number 60-11656  
M
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3
. Secure the cover plate (if used) and subbase with the  
screws provided. Do not fully tighten the subbase screws.  
. Level the subbase using a spirit level, as shown in  
Fig. 1—Installation of subbase on outlet box.  
4
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.  
Fig. 3—Subbase components and leveling  
procedure.  
For a wall installation, hold subbase in position and  
mark holes for anchors. See 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  
WIRING THE SUBBASE  
until flush with the wall.  
All wiring must comply with local electrical codes and  
ordinances. Follow equipment manufacturer wiring in-  
structions when available. To wire subbase, proceed as  
follows:  
Fig. 2—Installation of subbase on wall.  
1. Connect the system wires to the subbase as shown in  
Figs. 8 through 16. A letter code is located near each  
terminal for identification. The terminal barrier permits  
straight or conventional wraparound wiring connections.  
See Fig. 4.  
Fig. 4—Wiring connections.  
2. Your Q674 Subbase can require one or more jumpers  
that may or may not be factory supplied. Refer to the wiring  
diagrams for specific terminals to be jumpered. See Table 3  
for proper application.  
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.  
CAUTION  
Never install more than one wire per terminal  
unless factory supplied jumper with spade termi-  
nal is used. See Fig. 7.  
IMPORTANT: Use 18 gauge, color-coded thermostat  
cable for proper wiring.  
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TABLE 3—JUMPER APPLICATIONS.  
If your subbase has: Application Use Fig.  
Fig. 6—Jumper adjacent terminals for special  
system hookup. Strip wire 3/4 in. [19 mm].  
RC, RH terminals  
single transformer  
system  
5
adjacent terminals  
special system  
operation or LED  
indication  
6
7
nonadjacent  
terminals  
3
4
. Firmly tighten each terminal screw.  
. Fit wires as close as possible to the subbase. Push  
excess wire back into the hole.  
5. Plug hole with nonflammable insulation to prevent  
drafts from affecting the thermostat.  
Fig. 5—Jumper RC and RH for single trans-  
former system. Strip wire 3/4 in. [19 mm].  
Fig. 7—For nonadjacent terminals, use jumper  
supplied with subbase.  
NOTE: Only the T874D Thermostat is shown with the  
subbases. Thisthermostat/subbaseprovides2-stageheat-  
ing and 2-stage cooling connections. If using another  
model, see Fig. 16 and Table 4.  
TABLE 4—THERMOSTAT BULB  
CONFIGURATOIN.  
Model No.  
T874A  
T874B  
T874C  
T874D  
T874E  
Heating Bulbs  
H1  
Cooling Bulbs  
C1  
H1  
C1,C2  
C1  
H1, H2  
H1, H2  
C1, C2  
C1, C2  
T874F  
H1, H2  
3
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Fig. 8—T874A-D/Q674A in standard heating/cooling system.  
Fig. 9—T874C,D/Q674B in standard heating/cooling system with separate transformers for heating and  
cooling.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1  
HOT)  
L2  
RH  
W1  
(
HEAT RELAY 1  
HEAT RELAY 2  
3
1
1
H1  
FAN  
SWITCH  
FALL  
AUTO  
W2  
H1 ANTICIPATOR  
ON  
HEAT CHANGEOVER  
VALVE  
4
B
H2  
X1  
6
8
FALL  
H2 ANTICIPATOR  
SYSTEM  
SWITCH  
O
COOL CHANGEOVER  
VALVE  
HEAT  
OFF  
C1  
RISE  
G
FAN RELAY  
9
2
COOL  
Y2  
COMPRESSOR  
CONTACTOR 2  
1
0
C1 ANTICIPATOR  
C2 ANTICIPATOR  
Y1  
1
1
COMPRESSOR  
CONTACTOR 1  
L2  
L1  
C2  
RC  
RISE  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD  
PROTECTION AS REQUIRED.  
(HOT)  
1
JUMPER RH, RC FOR SINGLE TRANSFORMER.  
3
OPTIONAL LED ON SOME MODELS.  
M933C  
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Fig. 10—T874D/Q674B in standard heating/cooling system with single transformer for heating and  
cooling. Exact replacement for York model no. 2TB04700324.  
Fig. 11—T874D,E,F/Q674C in standard heating/cooling system.  
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Fig. 12—T874A,D,F/Q674D in standard heating/cooling system.  
Fig. 13—T874D/Q674E in standard heating/cooling system.  
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Fig. 14—T874A-F/Q674G in standard heating/cooling system.  
Fig. 15—T874C/Q674B in standard application.  
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Fig. 16—Typical Q674 terminal designations. The thermostat and subbase used determines the number  
of system components controlled.  
TEMPERATURE LEVER STOPS  
Some thermostats have factory-installed temperature  
INSTALL AND ADJUST LOCKING LEVER  
SCREWS  
lever locking screws (Fig. 17) and/or stop brackets  
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.  
(
Fig. 18). Use these only if the HEAT and COOL tempera-  
ture set point lever ranges are to be restricted. If the compo-  
nents are factory-installed, see the specific section below  
for the adjustment procedure.  
If a temperature range restriction is required and the  
locking components are not factory-installed, it is neces-  
sary to order a 4074ECK Envelope Assembly. This enve-  
lope includes two stop brackets, one brass insert and one  
bracket mounting screw for restricting the adjustable range  
of the HEAT and COOL set point levers. Also, the enve-  
lope includes two screws with plastic insulated heads for  
locking the set point control levers in position. If the  
components are to be used, see the specific section below  
for the installation procedure.  
To install:  
1. Refer to Fig. 20 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  
Install the stop brackets only if there is a need to restrict  
the adjustable range of the heating and cooling temperature  
set point levers.  
Fig. 17—Location of lever locking screws.  
To install:  
LEVER LOCKING SCREWS  
1. Turn to the back of the T874 Thermostat. Locate the  
hole for the brass insert in the plastic base below the LED  
window. See Fig. 19.  
2
3
4
. Push the brass insert into the hole with your finger.  
. Turn to the front of the T874 Thermostat.  
. Place the two stop brackets in position with the tabs  
in the slot between the HEAT and COOL levers. See  
Fig. 20.  
M18680  
5
. Insert the mounting screw into the two slots in the  
Fig. 18—Location of lever stop brackets.  
stop brackets and attach to the brass insert. Tighten the  
screw to pull the brass insert into the back of the thermostat.  
LEVER STOP BRACKETS  
6
. Loosen the mounting screw enough so the stop brack-  
ets can slide for adjustment.  
. Move the HEAT and COOL set point levers to the  
maximum temperature that is desired.  
. Slide the stop brackets until one rests against the  
HEAT lever and the other against the COOL lever.  
7
8
M18681  
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9
. Firmly tighten the mounting screw.  
MOUNTING THE THERMOSTAT  
1. Remove the thermostat cover by pulling the bottom  
edge of the cover upward until it snaps free of the cover clip.  
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.  
NOTE: The cover is hinged at the top and must be removed  
by pulling up at the bottom.  
CAUTION  
2. Carefully remove and discard the polystyrene packing  
insert that protects the mercury switches during shipment.  
Do not use standard screws that provide metal-to-  
metal contact with the stop brackets. Short circuit  
and potential equipment damage may result.  
3. Turn over the thermostat base and note the spring  
fingers that engage the subbase contacts. Make sure the  
spring fingers are NOT bent flat, preventing proper electri-  
cal contact with the subbase.  
4. Set the adjustable heat anticipator indicators to the  
Fig. 19—Installing brass insert.  
respective current setting for each stage. See Setting the  
Heat Anticipator section.  
5
. Note the two tabs on the top inside edge of the  
LED WINDOW  
thermostat base. The tabs fit into corresponding slots on top  
of the subbase. Mount the thermostat on the subbase.  
6. Align the two captive mounting screws in the ther-  
mostat base with the posts on the subbase. See Fig. 21.  
Tighten both screws. Do not overtighten screws or damage  
to subbase posts can result.  
Fig. 21—Mounting thermostat on subbase.  
BRASS INSERT  
INSERT HOLE  
BACK OF  
THERMOSTAT  
M955A  
Fig. 20—Installing stop brackets.  
HOLES FOR INSULATED  
LOCKING LEVER SCREWS  
COOL  
LEVER  
HOLE WITH  
BRASS INSERT  
HEAT  
LEVER  
BRACKET  
TABS  
Settings  
SETTING THE HEAT ANTICIPATOR  
Move the indicator to match the current rating of the  
primary contro. See Fig. 22. When using the T874 Thermo-  
stat 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 and use the  
following procedure to determine the current draw of each  
stage.  
ADJUSTABLE  
LEVER STOP  
BRACKETS  
MOUNTING  
SCREW  
BRACKET  
SLOTS  
The current draw must be measured with the thermostat  
removed from the subbase and the power on to the heating  
system.  
M18682  
1. Connect an ac ammeter of appropriate range between  
the heating terminals of the subbase:  
Stage 1: between W1 and RH or R.  
Stage 2: between W2 and RH or R.  
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2
. Move the system switch to AUTO or HEAT (if  
SUBBASE SETTING  
used).  
The subbase switching positions control the system  
operation as described below (Fig. 23).  
SYSTEM SWITCH (some subbases 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, fan is also off.  
AUTO: Thermostat automatically changes between  
heating and cooling system operation, depending  
on the indoor temperature.  
HEAT: Heating system is automatically controlled  
by the thermostat. Cooling system is off.  
COOL: Cooling system is automatically controlled  
by the thermostat. Heating system is off.  
FAN SWITCH  
3. After one minute, read the ammeter and record the  
reading:  
Stage 1: __________ amperes.  
Stage 2: __________ amperes.  
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  
2
-stage heating equipment is designed to operate at three  
cycles per hour per stage, and 1-stage heating equipment  
at six cycles per hour, at 50 percent load condition.  
When using the T874 Thermostat in heat pump systems,  
set the heat anticipator at 140 percent of the actual  
primary control current draw to reduce the cycling rate.  
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.  
Fig. 22—Adjustable heat anticipator scales.  
Checkout  
HEATING  
Move the system switch on the subbase to AUTO or  
HEAT (if used) and the fan switch to AUTO. Move the  
heating set point lever on the thermostat about 10° F [6° C]  
above room temperature. Heating should start and the fan  
should start after a short delay. Fan starts immediately in  
heat pump systems. Move the heat lever 10° F [6° C] below  
room temperature. The heating should shut off; fan should  
shut off after a short delay. Fan shuts off immediately in  
heat pump systems.  
Most heat pump systems should cycle 2-1/2 to 3 times  
per hour.  
. Hang the upper edge of the thermostat cover on top of  
4
the thermostat base and swing the cover downward until it  
engages with the cover clip.  
TEMPERATURE SETTING  
NOTE: In heat pump applications, time delays are involved  
before the compressor is activated to prevent short cy-  
cling. The delays are provided by a minimum-off timer  
that prevents the compressor from starting for up to five  
minutes from when the thermostat last turned off the  
compressor, or from when the system first received  
power.  
Move the heating and cooling set point levers (Fig. 23)  
to the desired comfort positions. One lever controls all  
stages of heating, and another lever controls all stages of  
cooling. The minimum differential between heating and  
cooling set point is 3° F [1.7° C].  
Fig. 23—Location of external components.  
COOLING  
Move the system switch on the subbase to AUTO or  
COOL (if used) and the fan switch to AUTO. Move the  
cooling set point lever on the thermostat about 10° F [6° C]  
below room temperature. The cooling and fan should start  
(
see NOTE above). Move the cool lever about 10° F [6° C]  
above room temperature. The cooling and fan should stop.  
FAN  
Move the subbase system switch to OFF, and the fan  
switchtoON. Thefanshouldruncontinuously. Movethefan  
switch to AUTO. In the AUTO position, fan operation is  
controlled by the heating or cooling system control circuit.  
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NOTE: Hand heat will offset the thermometer reading.  
After making each adjustment, wait ten minutes for the  
thermometer to stabilize before comparing.  
Calibration  
THERMOSTAT  
T874Thermostatsareaccuratelycalibratedatthefactory.  
They do not have provision for field calibration.  
Fig. 24—Thermometer calibration.  
THERMOMETER  
The thermometer in the thermostat has been accurately  
calibrated at the factory. The thermometer should need ad-  
justment only if it has been dropped or shifted due to mishan-  
dling.  
If the set point lever and the thermometer reading do not  
agree, use the following procedure:  
1
. Remove the thermostat cover by pulling up from the  
bottom of the cover until it clears the mounting slots.  
. Set the thermostat cover on a table near an accurate  
thermometer.  
2
3. Allowtenminutesforcoverthermometertosensearea  
temperature; compare the readings. Be careful not to touch  
the thermometer or breathe on it.  
4
. If the readings are the same, replace cover and put the  
system into operation.  
. If the readings are different, insert a small screwdriver  
5
in the thermometer slot (Fig. 24) and turn it until the ther-  
M5070  
mometers have the same reading.  
6. Replace thermostat cover and put the system into  
operation.  
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