Honeywell Q674B User's Manual

Honeywell Thermostats User's Manual - Q674B.
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X-XX UL

INSTALLATION INSTRUCTIONS

Copyright © 1996 Honeywell Inc.  •            •   All Rights Reserved

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.

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.

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.

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.

INSTALLATION

When Installing this Product…

 Read these instructions carefully. Failure to follow

them could damage the product or cause a hazard-
ous 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.

69-0087-6

T874 Model

Stage

Ha

Q

W

Heating Stages

1

1

3

Cooling Stages

1

2

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

0.502419s