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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
The T874H,Q,W Multistage Thermostats provide 24 to 30
has failed, and the heat pump is not operating. The
Vac control for heating and cooling systems as listed in
LED lights when the homeowner places the system
Table 1.
switch in the EM. HT. position.
A
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES VERTICAL MOUNTING OUTLET SCREWS (2) 1 CAUTION BOX 1. Disconnect the power supply to prevent COVER ADAPTER PLATE 2 electrical shock or equipment damage. RING 2 2. Run the wires as close as possible to the subbase. To prevent interference with the thermostat linkage, keep the wire length to a minimum. Push the excess wire back into the hole, and plug the hole to prevent drafts from affecting the thermostat operation. 1 HORIZONTAL 3. Do not
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES FOR STRAIGHT FOR WRAPAROUND– Mounting C815A Thermistor (T874W only) INSERTION– STRIP 5/16 in. (8 mm) STRIP 7/16 in. (11 mm) The T874W is used with the C815A Thermistor mounted in the outdoor section. Locate it in an area where it can measure the true outdoor ambient temperature. Avoid mounting the C815A in an area where it is exposed to high temperatures or direct sunlight. Refer to heat pump BARRIER equipment instructions for proper moun
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS H1 ANTICIPATOR 1 W1 NO FAN 3 CHANGEOVER SWITCH RELAY FALL B H1 4 W2 H2 ANTICIPATOR FAN RELAY 6 G FALL SYSTEM H2 Y1 SWITCH 8 OFF 1 COMPRESSOR CONTACTOR L2 9 AUTO C1 R L1 (HOT) 1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND C1 ANTICIPATOR OVERLOAD PROTECTION AS REQUIRED. 10 M6008A RISE Fig. 6. T874Q/Q674G for heating only system. THERMOSTAT SUBBASE SYSTEM COMPONENTS 1 L1 (HOT) 1 H1 ANTICIPATOR R C815A
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS L1 1 (HOT) FALL 1 L2 H1 ANTICIPATOR T H1 2 C815A OD THERMISTOR W3 H2 H2 ANTICIPATOR AUX. HEAT RELAY FALL 3 U AUXILIARY FAN SWITCH HEAT LED (GREEN) H3 ANTICIPATOR AUTO G 4 ON FAN RELAY EMERGENCY H3 HEAT LED R FALL (RED) 5 E 6 EM. HEAT RELAY RESET COMPRESSOR MONITOR L CHECK LED (RED) RISE X 8 SYSTEM SWITCH B C1 EM.HEAT CHANGEOVER 2 9 RELAY (HEAT) CHANGEOVER HEAT RELAY (COOL) C1 ANTICIPATOR OFF 10
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES THERMOSTAT SUBBASE SYSTEM COMPONENTS 1 FALL H1 ANTICIPATOR T H1 2 C815A OUTDOOR THERMISTOR W3 H2 H2 ANTICIPATOR FALL AUX. HT. RELAY 3 FAN SWITCH AUX. HEAT LED (GREEN) AUTO H3 ANTICIPATOR G 4 ON FAN RELAY H3 L1 R (HOT) FALL 5 L2 EM. HEAT 1 LED (RED) E 6 EM. HT. RELAY RESET X1 CHECK LED (YELLOW) C RISE CHANGEOVER RELAY (HEAT) 2 8 SYSTEM SWITCH B C1 CHANGEOVER EM.HT. RELAY (COOL) 9 HEAT O C1 ANTICIPATOR OFF 10 X2 COMPRESSOR COOL CONTACT
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES 4600 SETTING 4400 4200 4000 C815A THERMISTOR RESISTANCE 3800 R = 400 ohms ± 10% AT 77°F (25°C) Setting the Heat Anticipator (T874Q Only) 3600 Set each heat anticipator to match its primary control 3400 3200 current draw. If the primary control nameplate has no 3000 rating or if further adjustment is necessary, use the 2800 2600 following procedure to determine the current draw of each 2400 stage. (Measure the current draw of each heating
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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES Fan (Select Models) NOTE: Hand heat offsets the thermometer Move the subbase system switch to OFF, and the fan reading. After making each adjustment, switch to ON. The fan runs continuously. When the fan wait 10 or 15 minutes for the thermometer switch is in the AUTO position, the fan operation is to stabilize before comparing. controlled by the heating or cooling system. CALIBRATION Thermostat T874 Thermostats are accurately calibrated a
