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Honeywell T874G Installation Instructions Manual

Thermostats and subbases for heat pump systems
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TRADELINE
The T874G Thermostats and Q674F,J Subbases pro-
vide 24 to 30 Vac control of 2-stage heating and 1-stage cool-
ing heat pump systems with automatic changeover. Stage 1
Thermostat/
Thermostat/
Subbase
Subbase
Model
Package
Numbers
Y594G1252
T874G1246/
Q674F1212
T874G1246/
Q674F1410
Y594G1419
T874G1642/
Q674F1444
c
Y594G1476
T874G1741/
Q674F1477
d
Y594G1534
T874G1824/
Q674F1477
Y594G1526
T874G1626/
Q674F1436
T874D1165
or
T874E1016/
Q674F1543
Y594G1567
T874G1865/
Q674J1209
c
Y594G1575
T874G1873/
Q674J1225
Y594G1633
T874G1972/
Q674F1584
a
EM.HT. also shows compressor malfunction.
b
When switch is in EM. HT. position, the emergency heat will operate continuously until system switch is moved to another position.
c
Thermostat is white and subbase is gray.
d
Sold only in Australia; degrees C.
e
LED indicator is not labeled but may be connected per user's requirements. See Fig. 9.
®
for Heat Pump Systems
Installation Instructions for the Trained Service Technician.
TABLE 1—THERMOSTAT/SUBBASE SPECIFICATIONS.
LED
Indication
AUX.HT.,
EM.HT.-OFF-
a
EM.HT.
HEAT-AUTO-
AUX.HT.,
EM.HT.
a
EM.HT.
HEAT-AUTO-
AUX.HT.,
OFF-EM.HT.-
EM.HT.,
HEAT-AUTO-
CHECK
AUX.HT.,
OFF-EM.HT.-
EM.HT.
HEAT-AUTO-
e
(RED)
OFF-EM.HT.-
HEAT-AUTO-
EM.HT.
EM.HT.-
AUTO-OFF
EM.HT.
EM.HT.-
AUTO-OFF
AUX.HT.,
OFF-EM.HT.-
EM.HT.
HEAT-AUTO-
J.H. • Rev. 7-94 •
T874G Thermostats
and Q674F,J Subbases
heat and cool anticipation is fixed voltage type; stage 2 heat
anticipation is adjustable (except as noted). See Table 1 for
specific T874G/Q674F,J combinations and specifications.
Switching
System
Fan
Changeover
AUTO-
ON
COOL
b
-OFF-
AUTO-
ON
COOL
AUTO-
ON
COOL
AUTO-
ON
COOL
AUTO-
ON
COOL
AUTO-
ON
AUTO-
ON
AUTO-
ON
COOL
• ©Honeywell Inc. 1994 • Form Number 69-0435—10
M3375
Comments
AUTO,
TRADELINE
COOL
AUTO,
Separate W1 and Y1
COOL
terminals; TRADELINE
subbase.
AUTO,
SUPER TRADELINE
HEAT OR
includes factory-installed
COOL
jumper across W1 and Y1;
fixed stage 2 heat anticipation.
Isolated CHECK LED
includes jumper for connecting
X2 terminal to X or R for
power.
AUTO,
TRADELINE
HEAT
AUTO
TRADELINE
replacement for York model
no. 2TB04700524. Thermostat
not included; order separately.
AUTO,
TRADELINE
COOL
replacement for York model
nos. 2TH11702424 and
6TH11702424.
AUTO,
TRADELINE
COOL
replacement for York model
nos. 2TH11702424 and
6TH11702424.
AUTO,
TRADELINE
HEAT OR
COOL
Application
See
Fig.
®
5
6
®
7
®
;
®
8
®
subbase; exact
9
®
; exact
10
®
; exact
10
®
11

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  Summary of Contents for Honeywell T874G

  • Page 1 Heat Pump Systems Installation Instructions for the Trained Service Technician. Application The T874G Thermostats and Q674F,J Subbases pro- heat and cool anticipation is fixed voltage type; stage 2 heat vide 24 to 30 Vac control of 2-stage heating and 1-stage cool- anticipation is adjustable (except as noted).
  • Page 2: Operation

    Operation IMPORTANT: Thermostats are calibrated at the factory by using subbases mounted at true level. Inaccurate sub- base leveling will cause thermostat control deviation. On a 2-stage heating thermostat, the two stages of heat make sequentially as the temperature drops. Make refers to LOCATION the mercury switch initiating a call for heat or cool.
  • Page 3 Fig. 2—Installation of Q674 Subbase on wall. Fig. 3—Subbase components and leveling procedure. TOP MOUNTING HOLES (2) WALL WIRING TERMINAL WIRES THROUGH THERMOSTAT WALL OPENING CABLE OPENING SPIRIT LEVEL WALL ANCHORS MOUNTING HOLES MOUNTING HOLES (2) POST (2) FOR SUBBASE MOUNTING TO SPRING FINGER CONTACTS THERMOSTAT...
  • Page 4 Fig. 5—Internal schematic and typical wiring diagram for Y594G1252 (T874G1246/Q674F1212); auto changeover in cooling. THERMOSTAT SUBBASE SYSTEM COMPONENTS H1 ANTICIPATOR (HOT) RTD1 OTD1 L2 1 SWITCH EHR1 RTD2 AUTO FALL ODT2 EHR2 RTD3 ANTICIPATOR FALL AUX. HEAT SYSTEM LED (GRN) SWITCH RTD1 SYSTEM...
  • Page 5 Fig. 7—Internal schematic and typical wiring diagram for Y594G1419 (T874G1642/Q674F1444), Y594G1476 (T874G1741/Q674F1477) and Y594G1534 (T874G1824/Q674F1477 sold only in Australia); auto changeover in heating and cooling; fixed anticipation. CHECK LED has isolated terminals. Factory- installed W1-Y1 jumper is equivalent to Y terminal. THERMOSTAT SUBBASE SYSTEM COMPONENTS...
  • Page 6 Fig. 8—Internal schematic and typical wiring diagram for Y594G1526 (T874G1626/Q674F1436); auto changeover in heating. THERMOSTAT SUBBASE SYSTEM COMPONENTS (HOT) L1 ODT 1 H1 ANTICIPATOR FALL RTD 1 EHR 1 RTD 2 FAN SWITCH ODT 2 AUTO EHR 2 RTD 3 ANTICIPATOR RTD 1 AUX.
  • Page 7 Fig. 10—Internal schematic and typical wiring diagram for Y594G1567 (T874G1865/Q674J1209) and Y594G1575 (T874G1873/Q674J1225); auto changeover in cooling. Exact replacement for York model nos. 2TH11702424 and 6TH11702424. THERMOSTAT SUBBASE SYSTEM COMPONENTS FALL COOL CHANGEOVER VALVE SWITCH H1 ANTICIPATOR AUTO FAN RELAY (HOT) H2 ANTICIPATOR FALL...
  • Page 8: Mounting The Thermostat

    MOUNTING THE THERMOSTAT The current draw must be measured with the thermo- 1. Remove the thermostat cover by pulling the bot- stat removed and the power on. tom edge of the cover away from the base until it snaps Do not short across primary control terminals. This free of the retaining posts.
  • Page 9 Checkout Calibration HEATING THERMOSTAT Move the system switch on the Q674 Subbase to T874 Thermostats are accurately calibrated at the HEAT. Move the heating set point lever on the T874 factory. They do not have provision for field calibration. Thermostat about 10° F [6° C] above room tempera- THERMOMETER ture.
  • Page 10 69-0435—10...
  • Page 11 69-0435—10...
  • Page 12 Home and Building Control Home and Building Control Honeywell Honeywell Limited—Honeywell Limitée 1985 Douglas Drive North 35 Dynamic Drive Golden Valley, Minnesota 55422 Scarborough, Ontario M1V 4Z9 69-0435–10 Printed in U.S.A.