Honeywell Q674G, Q674B, Q674C User Manual

T874H,Q,W Multistage Thermostats and

Q674B,C,G,L Subbases

INSTALLATION INSTRUCTIONS

APPLICATION

The T874H,Q,W Multistage Thermostats provide 24 to 30 Vac control for heating and cooling systems as listed in Table 1.

Table 1. Heating and Cooling Stages.

T874 Model

Stage H

Heating Stages 1 1 3 Cooling Stages 1 — 2

Plus a changeover stage that operates with cooling.

The Q674B,C,G,L Subbases provide wiring terminals, system and fan switching, and mounting bases for T874 Multistage Thermostats as listed in Table 2.

Table 2. Switching Positions.

Q674

Model

B Heat-Off-Cool Auto-On C Off-Auto Auto-On

G Off-Auto None

L Em Ht-Heat-Off-Cool Auto-On

System Fan

Switch Positions

OPERATION

On a two-stage or three-stage heat thermostat, the stages of heat

make

refers to the mercury switch initiating a call for heat or cool.

There are about 2°F (1°C) between the stages so that the second stage makes only when the first stage can not handle the load. About one degree later, the third stage makes (T874W only). This degree difference is called the

interstage differential

Select models include LEDs (light-emitting diodes). The LED lights to indicate a problem with the system; refer to the system manufacturer instructions.

sequentially as the temperature drops.

Make

When an LED lights, refer to this list for the meaning:

FILTER: clogged filter needs replacement. EM. HT.: emergency heat is operating. The compressor

has failed, and the heat pump is not operating. The LED lights when the homeowner places the system switch in the EM. HT. position.

AUX. HT.: auxiliary heat is operating because the

weather is so cold that the heat pump alone cannot handle the load.

SERVICE or CHECK: system needs to be checked.

See heating system instructions for specific meaning.

LEDs are not field addable or replaceable.

RECYCLING NOTICE

This control contains mercury in a sealed tube. Do not place the 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 control in the trash.

Contact your local waste management authority for instructions regarding the recycling and the proper disposal of this control, or of an old control containing mercury in a sealed tube.

INSTALLATION

When Installing this Product…

 Read these instructions carefully. Failure to follow

them could damage the product or cause a hazardous condition.

 Check the ratings given in the instructions and on

the product to make sure the product is suitable for your application.

 Installer must be a trained, experienced service

technician.

 After installation is complete, check out product

operation as provided in these instructions.

not

place your old

X-XX UL

69-0087-6

T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES

CAUTION

1. Disconnect the power supply to prevent electrical shock or equipment damage.

2. Run the wires as close as possible to the subbase. To prevent interference with the thermostat linkage, keep the wire length to a minimum. Push the excess wire back into the hole, and plug the hole to prevent drafts from affecting the thermostat operation.

3. Do not tighten the thermostat captive mounting screws to the point of damaging the subbase threads.

4. Do not short across the coil terminals on the relay. This can burn out the heat anticipator.

5. Never install more than one wire per terminal unless a factory-supplied jumper with a spade terminal is used.

IMPORTANT

These thermostats are calibrated at the factory by using subbases mounted at true level. Inaccurate subbase leveling causes thermostat control deviation.

Location

Install the thermostat about 5 ft (1.5m) 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 behind the thermostat

such as an outside wall.

Mounting and Wiring the Subbase

Mount the subbase on a wall or horizontal outlet box. If you mount it on a vertical outlet box, order Honeywell part no. 193121A Adapter Assembly, which includes an adapter ring with two screws, and a cover plate to cover the marks on the wall.

All wiring must comply with local electrical codes and ordinances. Follow the equipment manufacturer wiring instructions, when available.

To install the subbase:

 Prepare a hole for the thermostat wires at the

chosen location. Run wires to the location.

 Pull about 6 in. (152 mm) of wire through the hole.

IMPORTANT

Use 18 gauge, color-coded thermostat cable for proper wiring.

 When mounting the subbase on a vertical outlet box,

install an adapter ring with the two screws provided with the adapter assembly. See Fig. 1.

 Pull the wires through the cover plate (if used) and

the subbase wire opening. Secure the cover plate and subbase with the two screws provided, but do not fully tighten.

 The subbase mounting slots provide for minor out-

of-level adjustments. Level the subbase by using a spirit level and tightening the subbase mounting screws. See Fig. 2.

VERTICAL OUTLET BOX

1 HORIZONTAL OUTLET BOX

SUBBASE

SUBBASE MOUNTING SCREWS (2)

CAPTIVE MOUNTING SCREWS (2)

1 NOT INCLUDED WITH UNIT.

2 ACCESSORY PARTS AVAILABLE (193121A).

MOUNTING SCREWS (2)

COVER PLATE

THERMOSTAT

THERMOSTAT COVER

ADAPTER RING

Fig. 1. Installation on vertical or horizontal outlet box.

SPIRIT LEVEL

MOUNTING HOLES (2)

TOP MOUNTING HOLES (2)

WIRING TERMINAL

POST (2) FOR MOUNTING THERMOSTAT

THERMOSTAT CABLE OPENING

TO SPRING FINGER CONTACTS ON THE THERMOSTAT (UP TO 12)

Fig. 2. Leveling subbase.

 Connect the system wires to the subbase. See Fig.

4 through 9. A letter code for identification is located near each terminal. The terminal barrier permits straight or conventional wraparound wiring connections. See Fig. 3. Either method is acceptable. Run the wires as close as possible to the subbase, keeping the wire length to a minimum. Push the excess wire back into the hole. Plug the hole to prevent drafts.

IMPORTANT

An incorrectly leveled subbase causes the temperature control to deviate from the setpoint.

M6009

M927

69-0087—6

T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES

Mounting C815A Thermistor (T874W only)

The T874W is used with the C815A Thermistor mounted in the outdoor section. Locate it in an area where it can measure the true outdoor ambient temperature. Avoid mounting the C815A in an area where it is exposed to high temperatures or direct sunlight. Refer to heat pump equipment instructions for proper mounting.

THERMOSTAT

H1 ANTICIPATOR

FALL

RISE

C1 ANTICIPATOR

RISE

POWER SUPPLY. PROVIDE DISCONNECT MEANS

AND OVERLOAD PROTECTION AS REQUIRED.

SERVICE LED ON SELECT MODELS.

FAN SWITCH

AUTO

SYSTEM SWITCH

OFF

AUTO

SUBBASE

SERVICE LED (YELLOW)

Fig. 4. T874H/Q674C in heating-cooling system.

FOR STRAIGHT INSERTION– STRIP 5/16 in. (8 mm)

SUBBASE TERMINAL SCREW

COMPRESSOR FAULT

FOR WRAPAROUND– STRIP 7/16 in. (11 mm)

BARRIER

Fig. 3. Wiring connections.

SYSTEM COMPONENTS

COOL CHANGEOVER VALVE

FAN RELAY

COMPRESSOR CONTACTOR

L1 (HOT)

M3680A

M928

THERMOSTAT

H1 ANTICIPATOR

FALL

RISE

C1 ANTICIPATOR

RISE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 5. T874H/Q674C in heating-cooling system with SERVICE LED and FILTER LED.

FAN SWITCH

AUTO

SYSTEM SWITCH

OFF

AUTO

SUBBASE

SYSTEM COMPONENTS

SERVICE LED (YELLOW)

FILTER LED (RED)

COOL CHANGEOVER VALVE

FAN RELAY

COMPRESSOR CONTACTOR

24 VAC

L1 (HOT)

M5902

69-0087—6

+ 5 hidden pages