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PRODUCT DATA
60- 2485- 8
® U.S. Registered Trademark
Copyright © 2001 Honeywell • All Rights Reserved
T874 Multistage Thermostats
and Q674 Subbases
APPLICATION
These thermostats and subbases provide low voltage control
of multistage heating and cooling systems, including heat
pump systems.
FEATURES
• T874 Thermostat has silent, dust-free mercury
switches operated by coiled bimetal elements.
• Heat anticipator(s) are adjustable or fixed cooling
anticipator(s) are fixed.
• Individual heat and cool levers and scales (most
models) for temperature setting located on top of
thermostat case.
• Cover thermometer on most T874 Multistage
Thermostat models.
• Locking cover and locking lever screws available for
T874 Multistage Thermostats.
• Versaguard™ Thermostat Guard or custom key lock
thermostat guards available for T874 Multistage
Thermostats.
• T874 Thermostat requires a Q674 Subbase.
• Q674 Subbase provides system and fan switching,
wiring terminals and mounting base for T874
Multistage Thermostat.
• Adapter plate available for mounting Q674 on wall or
horizontal outlet box.
• Light-emitting diodes (LEDs) located on subbase for
easy reference.
• Up to three stages each of heating and cooling control
possible.
• Models with setpoint restrictions and locking cover
with no thermometer available for Department of
Defense (DoD) and other special applications.
• Outdoor reset used on some models to improve
thermal performance.
Contents
Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Understanding Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Cross Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96