Honeywell Q674G, Q674B, Q674C User Manual

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T874H,Q,W Multistage Thermostats and

Q674B,C,G,L Subbases

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

Ha

 

Q

 

W

Heating Stages

1

 

1

 

3

 

 

 

 

 

 

Cooling Stages

1

 

 

2

 

 

 

 

 

 

a 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

Switch Positions

Model

System

Fan

 

 

 

B

Heat-Off-Cool

Auto-On

 

 

 

C

Off-Auto

Auto-On

 

 

 

G

Off-Auto

None

 

 

 

L

Em Ht-Heat-Off-Cool

Auto-On

 

 

 

INSTALLATION INSTRUCTIONS

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 not place your old 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.

OPERATION

On a two-stage or three-stage heat thermostat, 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 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.

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.

Copyright © 1996 Honeywell Inc. •

• All Rights Reserved

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 MOUNTING

OUTLET SCREWS (2)

BOX 1

COVER

ADAPTER PLATE 2

RING 2

1 HORIZONTAL OUTLET BOX

 

 

 

 

THERMOSTAT

 

 

COO

L

THERMOSTAT

 

 

80

 

COVER

 

 

60 70

 

 

 

50

 

 

SUBBASE

 

70

 

 

 

 

80

 

 

 

 

60

 

 

 

HEA

T 50

 

 

 

 

 

 

SUBBASE

 

 

 

 

MOUNTING SCREWS (2)

 

 

 

 

 

 

 

 

80

 

70

CAPTIVE

60

50

MOUNTING SCREWS (2)

 

1 NOT INCLUDED WITH UNIT.

2 ACCESSORY PARTS AVAILABLE (193121A).

M6009

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

 

 

TOP

WIRING

THERMOSTAT

 

 

MOUNTING

TERMINAL

CABLE OPENING

SPIRIT LEVEL

HOLES (2)

 

 

 

 

 

 

 

 

 

MOUNTING

POST (2) FOR

TO SPRING FINGER

HOLES (2)

MOUNTING

CONTACTS ON THE

 

THERMOSTAT

THERMOSTAT

 

 

 

(UP TO 12)

M927

 

 

 

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.

69-0087—6

2

Honeywell Q674G, Q674B, Q674C User Manual

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.

FOR STRAIGHT

FOR WRAPAROUND–

INSERTION–

STRIP 5/16 in. (8 mm)

STRIP 7/16 in. (11 mm)

BARRIER

 

SUBBASE TERMINAL SCREW

M928

Fig. 3. Wiring connections.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2

 

Y1

 

 

H1

 

 

 

 

 

 

FALL

ANTICIPATOR

 

 

 

COOL CHANGEOVER

 

3

 

 

 

VALVE

 

H1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FAN SWITCH

 

 

 

 

 

 

4

AUTO

 

 

 

FAN RELAY

 

 

 

 

 

 

 

 

 

 

 

 

G

 

 

 

 

 

ON

 

R

 

 

 

 

 

 

 

 

 

 

 

 

SYSTEM

 

Y2

 

 

 

 

8

 

 

 

 

 

 

SWITCH

 

 

 

COMPRESSOR

 

 

 

 

 

 

 

 

 

OFF

 

 

 

 

 

 

 

B

 

CONTACTOR

 

RISE

9

AUTO

 

 

 

 

 

 

 

 

 

 

 

C1

 

 

 

 

 

 

 

ANTICIPATOR

 

 

 

 

 

 

CO

 

 

 

 

 

1

 

 

10

 

 

O

L1

L2

 

 

 

 

 

 

(HOT)

 

RISE

 

2

X

 

 

 

 

 

 

 

 

C1

 

 

SERVICE LED

 

COMPRESSOR

 

 

 

 

 

 

 

 

 

 

 

(YELLOW)

 

 

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS

 

FAULT

 

 

 

 

 

AND OVERLOAD PROTECTION AS REQUIRED.

 

C

 

 

 

 

 

 

 

 

 

2 SERVICE LED ON SELECT MODELS.

M3680A

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

 

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

 

2

 

Y1

 

H1 ANTICIPATOR

FAN SWITCH

COOL CHANGEOVER

H1

 

3

VALVE

 

 

FALL

AUTO

G

 

 

4

ON

FAN RELAY

 

 

 

R

 

 

 

COMPRESSOR

 

 

 

CONTACTOR

 

RISE

 

Y2

 

 

 

 

 

 

B

CO

8

 

 

 

 

 

 

 

 

O

 

9

SYSTEM

X

 

 

SWITCH

 

 

 

 

C1 ANTICIPATOR

 

SERVICE

 

OFF

LED (YELLOW)

 

10

 

 

X1

 

 

AUTO

C1

RISE

 

 

 

 

C

 

 

 

 

 

 

24 VAC

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS

FILTER LED (RED)

AND OVERLOAD PROTECTION AS REQUIRED.

X2

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

1

L2

L1 (HOT)

M5902

3

69-0087—6

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