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T874A-F Multistage Thermostats
The T874A-F Thermostats provide 24 to 30 Vac control
for heating and/or cooling systems. See Tables 1 and 2.
TABLE 1—HEATING AND/OR COOLING STAGES.
T874
A
Heating Stages
1
Cooling Stages
1
The Q674A-E,G Subbases provide wiring terminals,
system and fan switching, and mounting bases for T874
Multistage Thermostats.
TABLE 2—SWITCHING POSITIONS.
Q674
Model
System
A
Heat-Auto-Cool
B
Heat-Off-Cool
C
Off-Auto
D
None
E
Off-Heat-Auto-Cool
G
Off-Auto
On a 2-heat thermostat, the two 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 stages so that the
second stage makes only when the first stage can not
handle the load. This is the interstage differential.
The LED indicators are light emitting diodes on the
subbase that light when something specific happens with-
in the system.
Up to four of the LEDs listed below may be included on
your subbase. When an LED lights, refer to the following
list for the meaning:
FILTER: Clogged filter needs replacement.
with Restricted Set Point
Installation Instructions for the Trained Service Technician.
Application
B
C
D
E
1
2
2
—
2
1
2
2
Switch Positions
Fan
Auto-On
Auto-On
Auto-On
None
Auto-On
None
Operation
S. M. • Rev. 6-93 •
Q674A-E,G Subbases
EM. HT.: Emergency heat is operating. The compres-
sor has failed, and the heat pump is not operating.
LED lights when system switch is placed in the EM.
HT. position.
AUX. HT.: Auxiliary heat is operating, which means the
weather is so cold that the heat pump can not handle
the load alone.
F
LOCKOUT: System is shut down and needs maintenance.
CHECK: System needs to be checked. See heating sys-
2
tem instructions for specific meaning.
—
SERVICE: See heating system instructions for specific
meaning.
LEDs are not field replaceable.
This control contains mercury in a sealed tube. Do not
place 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 recycling and the proper disposal of
this control, or of an old control containing mercury in a
sealed tube.
WHEN INSTALLING THIS PRODUCT...
1. Read these instructions carefully. Failure to fol-
low them could damage the product or cause a hazardous
condition.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for your
application.
3. Installer must be a trained, experienced service
technician.
4. After installation is complete, check out the product
operation as provided in these instructions.
1
• ©Honeywell Inc. 1993 • Form Number 60-1227—1
M3375
Recycling Notice
M3375
Installation
60-1227—1
Related Manuals for Honeywell t874a-f
Summary of Contents for Honeywell t874a-f
- Page 1 LED lights when system switch is placed in the EM. The T874A-F Thermostats provide 24 to 30 Vac control HT. position. for heating and/or cooling systems. See Tables 1 and 2.
- Page 2 The thermostat subbase can be mounted on a vertical outlet box, horizontal outlet box or directly on the wall. 1. To mount on a vertical outlet box, order Honeywell 193121A Adapter Assembly. See Fig. 1. The assembly includes an adapter ring, two screws and a cover plate to...
- Page 3 WIRE THE SUBBASE Disconnect power supply before beginning installation Fig. 4—Wiring connections. to prevent electrical shock or equipment damage. All wiring must comply with local electrical codes and ordinances. Follow equipment manufacturer’s wiring instructions when available. To wire the subbase, proceed as follows: FOR STRAIGHT INSERTION–...
- Page 4 Fig. 6—T874D/Q674B in standard heating/cooling system. L1 (HOT) FALL HEAT RELAY 1 SWITCH AUTO H1 ANTICIPATOR HEAT RELAY 2 H2 ANTICIPATOR HEAT DAMPER OR FALL CHANGEOVER RELAY RISE COOL DAMPER OR CHANGEOVER RELAY SYSTEM SWITCH HEAT FAN RELAY ANTICIPATOR COOL COMPRESSOR CONTACTOR 2 C2 ANTICIPATOR...
- Page 5 Fig. 8—T874D/Q674D in standard heating/cooling system. (HOT) FALL HEAT RELAY 1 H1 ANTICIPATOR HEAT RELAY 2 SWITCH H2 ANTICIPATOR FALL RISE SYSTEM SWITCH C1 ANTICIPATOR COMPRESSOR CONTACTOR 2 C2 ANTICIPATOR COMPRESSOR CONTACTOR 1 (HOT) RISE POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. JUMPER RC, RH FOR SINGLE TRANSFORMER.
- Page 6 Fig. 10—T874D/Q674G in standard heating/cooling system. FALL (HOT) NO FAN H1 ANTICIPATOR HEAT RELAY 1 SWITCH ANTICIPATOR FALL HEAT RELAY 2 RISE SYSTEM SWITCH COMPRESSOR CONTACTOR 2 AUTO ANTICIPATOR COMPRESSOR ANTICIPATOR CONTACTOR 1 RISE (HOT) POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. JUMPER RC, RH FOR SINGLE TRANSFORMER.
- Page 7 MOUNTING THE THERMOSTAT 1. Remove the thermostat cover by pulling the bottom Fig. 12—Restricted set point. edge of the cover upward until it snaps free of the cover clip. NOTE: The cover is hinged at the top. Remove it by pull- ing up at the bottom.
- Page 8 Home and Building Control Home and Building Control Helping You Control Your World Honeywell Inc. Honeywell Limited—Honeywell Limitée 1985 Douglas Drive North 740 Ellesmere Road Golden Valley, MN 55422 Scarborough, Ontario M1P 2V9 QUALITY IS KEY Printed in U.S.A.