Honeywell T874H Multistage Thermostat Instruction Manual
T874H,Q,W Multistage Thermostats and
Q674B,C,G,L Subbases
INSTALLATION INSTRUCTIONS
When an LED lights, refer to this list for the meaning:
APPLICATION
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.
The T874H,Q,W Multistage Thermostats provide 24 to 30
Vac control for heating and cooling systems as listed in
Table 1.
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.
Table 1. Heating and Cooling Stages.
T874 Model
a
Stage
H
Q
1
W
3
Heating Stages
Cooling Stages
1
1
—
2
LEDs are not field addable or replaceable.
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.
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.
Table 2. Switching Positions.
Switch Positions
System
Q674
Model
If this control is replacing a control that contains
mercury in a sealed tube, do not place your old
control in the trash.
Fan
B
C
G
L
Heat-Off-Cool
Off-Auto
Auto-On
Auto-On
None
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.
Off-Auto
Em Ht-Heat-Off-Cool
Auto-On
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.
INSTALLATION
When Installing this Product…
³
Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard-
ous condition.
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.
·
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.
Select models include LEDs (light-emitting diodes). The
LED lights to indicate a problem with the system; refer to
the system manufacturer instructions.
69-0087-6
| General | Details |
|---|---|
| Name | Honeywell T874H Multistage Thermostat Instruction Manual |
| Make | Honeywell |
| Language | English |
| Filetype | PDF (Download) |
| File size | 0.19 MB |
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Honeywell T874H Manual: Questions and Answers
Where is the wire opening on the Honeywell T874H thermostat subbase located?
At the top of the subbase, where wires enter before connecting to terminals. Instruction Manual, p. 2
What is the minimum wire gauge required for the Honeywell T874H?
18 gauge, color-coded thermostat cable. Instruction Manual, p. 2
What voltage does the Honeywell T874H provide for heating and cooling control?
24 to 30 Vac. Instruction Manual, p. 1
How do I mount the Honeywell T874H subbase on a vertical outlet box?
Order Honeywell adapter assembly part no. 193121A, which includes an adapter ring and cover plate.
- Install the adapter ring with the two screws provided on the vertical outlet box.
- Pull wires through the cover plate and subbase wire opening.
- Secure the cover plate and subbase with the two screws provided, but do not fully tighten.
- Level the subbase using a spirit level, then tighten the mounting screws. Instruction Manual, p. 2
How do I level the Honeywell T874H subbase correctly?
Use a spirit level to check alignment, then tighten the subbase mounting screws.
- Place a spirit level on the subbase.
- Adjust the subbase position using the mounting slots for minor out-of-level corrections.
- Tighten the mounting screws once level is achieved. Instruction Manual, p. 2
Can the LEDs on the Honeywell T874H be replaced or added in the field?
No. LEDs are not field addable or replaceable. Instruction Manual, p. 1
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