Honeywell t841a Installation Instructions Manual page 12

T841A HEATING-COOLING THERMOSTATS
CHECKOUT
Heating
Move the system switch on the thermostat to HEAT and
the fan switch to AUTO. Move the setpoint lever about
10°F (6°C) above room temperature. Heating should start
and the fan should run. Move the setpoint lever about 10°F
(6°C) below room temperature. Heating and fan should
shut off.
NOTE: In heat pump applications, compressor activation
is time delayed to prevent short cycling. The
minimum-off timer controls the delays and
prevents the compressor from starting for up to
five minutes, either from when the thermostat last
turned off the compressor, or from when the
system first received power.
Cooling
A CAUTION
If outdoor temperature is below 50°F (10°C), do
not operate cooling. Refer to manufacturer's
recommendations.
Move the system switch on the thermostat to COOL and
the fan switch to AUTO. Move the set point lever about
10°F (6°C) below room temperature. Cooling should start,
followed by the fan (see NOTE above). Move the set point
lever about 10°F (6°C) above room temperature. Cooling
and fan should shut off.
Fan
Move the system switch to OFF, and the fan switch to ON.
The fan should run continuously. Move the fan switch to
AUTO. In this position, fan operation is controlled by the
heating or cooling system control circuit.
Automation and Control Solutions
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Outdoor Reset Thermistor (Honeywell
C815A1005)
For system shown in Fig. 5, the thermistor must be used; if
not, thermostat performance deviates radically from proper
operation.
The proper thermostat operation must be verified to assure
the correct operation of the thermostat. Check thermistor
operation as follows:
1. Disconnect the Twire on the thermostat.
2. Use an ohmmeter to measure resistance between
the Twire and the ^th e rm o s ta t terminal.
3. Take outdoor temperature at thermistor location and
find the correct thermistor resistance on the chart in
Fig. 19.
4. If the resistance measured in step 2 and the
calculated resistance in step 3 vary by more than 15
percent, the thermistor requires replacement.
Contact Original Equipment Manufacturer or
installation dealer for outdoor thermistor
replacement.
-20 0 20
TEMPERATURE OF THERMISTOR (°F)
Fig. 19. Thermistor resistance chart.
40 60 80 100 120
M1590A
Honeywell
www.honeywell.com/yourhome
140