69-0392—9
9
T874R THERMOSTATS AND Q674L SUBBASES
M5070
CHECKOUT
Heating
Move the system switch on the Q674 Subbase to HEAT.
Move the setpoint lever on the T874 Thermostat about
10° F (6° C) above room temperature. Both stages of
heating and the fan should start. Move the setpoint lever
about 10° F (6° C) below room temperature. Heating and
fan should shut off.
NOTE: To prevent compressor short cycling, some
manufacturer equipment includes a minimum-off
timer to provide a five-minute time delay before
turning on the compressor after the thermostat
last turned off the compressor, or after the
system first received power. This delay protects
the compressor.
Cooling
CAUTION
Do not operate cooling if the outdoor temperature
is below 50° F (10° C). Refer to manufacturer
recommendations.
Move the system switch on the Q674 Subbase to COOL.
Move the setpoint lever on the T874 Thermostat about
10° F (6° C) below room temperature. Cooling and fan
should start (see NOTE above). Move the setpoint lever
about 10° F (6° C) above room temperature. Cooling and
fan should stop.
Emergency Heat
Move the system switch to EM.HT. The EM.HT. LED
should come on. Move the setpoint lever about 10° F
(6° C) above room temperature. The electric strip heater(s)
should come on. Move the setpoint lever about 10° F
(6° C) below room temperature. The electric strip heater
should de-energize. The EM.HT. LED remains on until
system switch is moved to another position.
Fan
Move the subbase system switch to OFF and the fan
switch to ON. The fan should run continuously. When the
fan switch is in the AUTO position, fan operation is con-
trolled by the heating or cooling system.
CALIBRATION
Thermostat
T874 Thermostats are accurately calibrated at the factory.
There is no provision for field calibration.
Thermometer
The thermometer in the thermostat has been accurately
calibrated at the factory. The thermometer should need
adjustment only if it was dropped or shifted due to
mishandling.
If the setpoint lever and the thermometer reading do not
agree:
1. Remove the thermostat cover by pulling out from the
bottom of cover until it clears the mounting slots.
2. Set the thermostat cover on a table near an
accurate thermometer.
3. Allow 10 or 15 minutes for cover thermometer to
sense area temperature; compare the readings. Be
careful not to touch thermometer or breathe on it.
4. If the readings are the same, replace cover and put
the system into operation.
5. If the readings are different, insert a small screw-
driver into the thermometer and turn it until the
thermometers have the same reading. See Fig. 15.
6. Replace thermostat cover and put the system into
operation.
NOTE: Radiant heat from hands offsets the thermometer
reading. After making each adjustment, wait 10
or 15 minutes for the thermometer to stabilize
before comparing.
Fig. 15. Thermometer calibration
(40 pages)
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