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®
TRADELINE
T874G Thermostats
and Q674F,J Subbases
for 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). See Table 1 for
ing heat pump systems with automatic changeover. Stage 1 specific T874G/Q674F,J combinations and specifications.
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IMPORTANT: Thermostats are calibrated at the factory by Operation 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. Install the thermostat about 5 ft [1.5 m] above the There are about 2° F [1° C] between stages so the floor in an area with good air circulation a
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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 (2) MOUNTING HOLES MOUNTING HOLES (2) SUBBASE POST (2) FOR MOUNTING TO SPRING FINGER CONTACTS MOUNTING THERMOSTAT ON THE THERMOSTAT M926 SCREWS (2) (UP TO 12) M927 IMPORTANT: Use 18 gauge, color-coded thermostat Fig. 4—Wiring Connections. cable for proper wiring. FOR STRAIGHT INSE
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Fig. 5—Internal schematic and typical wiring diagram for Y594G1252 (T874G1246/Q674F1212); auto changeover in cooling. THERMOSTAT SUBBASE SYSTEM COMPONENTS L1 H1 ANTICIPATOR R (HOT) 2 RTD1 OTD1 FAN L2 1 SWITCH 3 EHR1 RTD2 AUTO 2 H1 FALL ON W3 4 ODT2 W2 H2 EHR2 RTD3 ANTICIPATOR 5 H2 FALL AUX. HEAT 6 SYSTEM LED (GRN) SWITCH RTD1 X OFF SYSTEM 8 MONITOR COOL EM. HEAT FAN L 9 LED (RED) RELAY AUTO G RISE C1 HEAT RD ANTICIPATOR COOL CHANGEOVER EM. HT. CHANGEOVER VALVE 10 O EM. HEAT RELAY RISE C1 E COM
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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 1 FAN 1 L1 L2 W3 RELAY SWITCH (HOT) CHANGEOVER W3 (HEAT) AUTO FAN RELAY 2 G ON FALL H1 ANTICIPATOR 3 R AUX. HEAT 4 FALL RELA
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Fig. 8—Internal schematic and typical wiring diagram for Y594G1526 (T874G1626/Q674F1436); auto changeover in heating. THERMOSTAT SUBBASE SYSTEM COMPONENTS (HOT) L1 L2 1 R ODT 1 H1 ANTICIPATOR FALL 2 RTD 1 EHR 1 RTD 2 H1 FAN SWITCH 3 ODT 2 AUTO 4 EHR 2 RTD 3 H2 ON ANTICIPATOR 5 W2 H2 RTD 1 FALL AUX. HEAT LED (GREEN) X SYSTEM EM. HT. SWITCH COMPRESSOR LED (RED) RD FAILURE OFF L 7 EM. HT. FALL G HEAT FAN RELAY AUTO B CHANGEOVER HEAT 8 CHANGEOVER COOL EM. HT. VALVE RELAY 9 E 10 EHT1 C1 ANTICIPAT
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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 O 2 FAN COOL CHANGEOVER VALVE SWITCH H1 H1 ANTICIPATOR G AUTO 3 FAN RELAY L1 ON (HOT) R 4 L2 1 H2 ANTICIPATOR FALL 5 W AUX. HEAT RELAY H2 6 SYSTEM SWITCH RISE X CO EM. HEAT RELAY 8 EM. HT. EM. HEAT LED (RED) AUTO B 9 COMPRESSOR OFF CO
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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. may burn out the heat anticipator. 1. Connect an ac ammeter of appropriate range be- NOTE: The cover is hinged at the top and must be tween the heating terminals of the subbase as follows: removed by pullin
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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- ture. Both stages of heating and fan should start. Move THERMOMETER the set point lever about 10° F [6° C] below room 1. Remove thermostat cover by pulling the bottom temperature. Heating and fan should s
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69-0435—10 10
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11 69-0435—10
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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.
