T874/Q674
Thermostat/Subbase Combinations
Installation Instructions for the Trained Service Technician.
Application
The T874/Q674 Thermostat/Subbase combinations provide 24 to 30 Vac control for heat pump systems. See Table 1. TABLE 1—T874/Q674 THERMOSTAT/SUBBASE COMBINATIONS.
Thermostat/ |
Number |
Changeover |
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Subbasea |
of Stages |
Stage |
Type of Switching |
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Model |
Heating |
Cooling |
Heating |
Cooling |
System |
Fan |
See Fig. |
T874N/Q674C |
2 |
1 |
1 |
— |
OFF-AUTO |
AUTO-ON |
5 |
T874N/Q674F |
2 |
1 |
— |
1 |
OFF-EM. HT.- |
AUTO-ON |
6 |
|
|
|
|
|
HEAT-AUTO-COOL |
|
|
T874R/Q674L |
2 |
1 |
— |
2b |
EM. HT.-HEAT- |
AUTO-ON |
7 |
|
|
|
|
|
OFF-COOL |
|
|
aQ674 Subbase provides the wiring terminals, system switch and fan switch for system operation.
bProvides manual changeover with the subbase system switch in COOL position.
Operation
On a two-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.
One or two LEDs (light emitting diodes) are included on your subbase. Refer to the list below for specific meaning.
The CHECK LED lights when something needs to be checkedordonetomaintain efficientoperationofthe system. See your heating system instructions for the specific meaning.
TheEM.HT.LEDlightswhenthesystemswitchisplaced in the EM. HT. position. Emergency heat is operating; in most systems, the compressor has failed and the heat pump is not operating.
The AUX. HT. LED lights when the auxiliary heat stage is operating. The weather is cold enough that the first stage cannot handle the load alone.
LEDs are not field replaceable or addable.
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 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.
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 and equipment damage.
2.Topreventinterferencewiththethermostatlinkage, keep wire length to a minimum and run wires as close as possible to the subbase. Push excess wire back into the hole and plug hole to prevent drafts from affecting thermostat operation.
3.Do not overtighten thermostat captive mounting screws because damage to subbase threads may result.
4.Do not short across coil terminals on the relay. This may burn out the thermostat heat anticipator.
IMPORTANT: Thermostats are calibrated at the factory using subbases mounted at true level. An inaccurately leveled subbase will cause thermostat control deviation.
S. M. • Rev. 5-93 • 
• ©Honeywell Inc. 1993 • Form Number 60-1147—4
LOCATION
Install the thermostat about 5 ft [1.5 m] above the floor in an area with good air circulation at average temperature.
Do not install the thermostat where it can 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 such as an outside wall behind the thermostat.
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 193121A Adapter Assembly (Fig. 1). The as-sembly includesanadapterring,twoscrewsandacoverplatetocover marks on the wall. Install the ring and cover plate on the vertical outlet box.
For a wall installation, hold subbase in position and mark holes for anchors (Fig. 2). Obtain wall anchors locally. Take care that the wires do not fall back into the wall opening. Set aside subbase. Drill four 3/16 in. [4.8 mm] holes and gently tap anchors into the holes until flush with the wall.
2.Pull wires through the cover plate (if used) and subbase cable opening (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, as shown in Fig. 3, and firmly tighten the 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 set point.
WIRING THE SUBBASE
IMPORTANT:Use18-gaugecolor-codedthermostatcable
for proper wiring.
Disconnect power supply before beginning installation to prevent electrical shock or equipment damage.
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. 5-7. A letter code located near each terminal is for identification. The terminal barrier permits straight or conventional wraparound wiring connection (Fig. 4).
2.Firmly tighten each terminal screw.
3.Fit wires as close as possible to the subbase. Push excess wire back into the hole.
4.Plug hole with nonflammable insulation to prevent drafts from affecting the thermostat.
MOUNTING THE THERMOSTAT
1. Remove the thermostat cover by pulling the bottom edge of the cover outward and away from the base until it snaps free of the mounting slots.
NOTE: The cover is hinged at the top and must be re-moved by pulling outward at the bottom.
Fig. 1—Installation of Q674 Subbase on outlet box.
VERTICAL |
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OUTLET |
1 |
BOX |
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ADAPTER |
COVER |
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PLATE |
2 |
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RING 2 |
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MOUNTING |
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SCREWS (2) |
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SUBBASE |
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MOUNTING |
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SCREWS (2) |
HORIZONTAL |
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OUTLET |
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BOX |
1 |
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SUBBASE |
MOUNTING |
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SCREWS (2) |
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1 NOT INCLUDED WITH UNIT. |
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2 ACCESSORY PARTS AVAILABLE (193121A). |
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M925 |
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Fig. 2—Installation of Q674 Subbase on wall.
WALL
WIRES THROUGH
WALL OPENING
WALL ANCHORS
(2)
|
MOUNTING |
|
HOLES |
|
SUBBASE |
|
MOUNTING |
M926 |
SCREWS (2) |
Fig. 3—Subbase components and leveling procedure.
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TOP MOUNTING HOLES (2) |
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WIRING |
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TERMINAL |
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THERMOSTAT |
SPIRIT LEVEL |
CABLE OPENING |
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MOUNTING HOLES (2) |
POST (2) FOR |
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TO SPRING FINGER CONTACTS |
MOUNTING |
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THERMOSTAT |
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ON THE THERMOSTAT |
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(UP TO 12) |
M927 |
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60-1147-4 |
2 |
2.Carefully remove and discard the polystyrene packing insert that protects the mercury switches during shipment.
3.If LED indication (EM.HT., CHECK, etc.) is to be used with the Q674 Subbase, install the preprinted insert under the thermostat set point scale (Fig. 8). To install, push both thermostatsetpointleverstothefarendsofthethermostat.Use index finger to gently pull out the plastic set point scale about 1/4 in. [6 mm]. Drop insert into recessed area behind set point scale so that selected LEDs show. Make sure insert is completelyseatedinrecessedarea.Letsetpointscalepopback,and set levers to desired positions.
Fig. 4—Wiring connections.
FOR STRAIGHT |
FOR WRAPAROUND– |
INSERTION– |
|
STRIP 5/16 in. [8 mm] |
STRIP 7/16 in. [11 mm] |
BARRIER |
|
SUBBASE TERMINAL SCREW |
M928 |
Fig. 5—Internal schematic and typical wiring diagram for T874N and Q674C.
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L1 |
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L2 (HOT) |
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1 |
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DEFROST RELAY |
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CONTACT |
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W1 |
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REVERSING |
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RELAY |
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OUTDOOR |
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THERMOSTAT |
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H1 |
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EM. HT. RELAY |
HEAT |
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CONTACT |
RELAY 2 |
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ANTICIPATOR |
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FALL |
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W3 |
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FAN |
EM. HT. RELAY |
HEAT |
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SWITCH |
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CONTACT |
RELAY 3 |
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H1 |
AUTO |
G |
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FALL |
ON |
FAN RELAY |
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H2 |
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R |
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H2 ANTICIPATOR |
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W2 |
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HEAT |
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SYSTEM |
RELAY 1 |
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SWITCH |
X |
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OFF |
CHECK |
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C1 |
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LED |
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AUTO |
(GRN) |
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ANTICIPATOR |
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L |
C1
CO
RISE
Y 
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
OPTIONAL
COMPRESSOR
FAILURE
DEVICE
COMPRESSOR
CONTACTOR
M1860
3 |
60-1147-4 |
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