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Thermistors
The 2800 series electric heat models use two
thermistors:
Room Air Temperature
Indoor Coil Temperature
The 3800 series (heat pump models) uses 4
thermistors:
Room Air Temperature
Indoor Coil Temperature
Outdoor Coil Temperature
Outdoor Air Temperature
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THERMISTOR
LEADS
The thermistors can be checked to determine if
they are good. Below is a chart showing thermistor
resistance values at various temperatures.
Thermistor Chart
Room Air Thermistor
Indoor Coil Thermistor
Outdoor Air Thermistor (3800 Model Series)
The outdoor air thermistor is located on a metal
bracket just behind the compressor. It detects the
temperature of the outdoor air being drawn into the
unit. The outdoor air thermistor is connected to the
control board at CN1 (blue wires).
Outdoor Coil Thermistor (3800 Model Series)
The outdoor coil thermistor is located in a copper
tube that is brazed to an end turn at the right side
of the outdoor coil. The outdoor coil thermistor is
connected to the control board at CN1 (black wires).
Outdoor Coil Thermistor
Outdoor Air Thermistor
Thermistor Location
Room Air Thermistor (2800 & 3800 Model Series)
The indoor air thermistor is located in front of the
indoor coil where it detects the temperature of
the room air being returned to the unit. It is held in
position away from the coil by a plastic fastener
that is pushed between the coil plate fi ns. The room
air thermistor is connected to the control board at
CN1 (yellow wires).
Indoor Coil Thermistor (2800 & 3800 Model Series)
The indoor coil thermistor is mounted in a copper
tube that is brazed to an end turn at the right side
of the indoor coil.
The indoor coil thermistor is connected to the control
board at CN1 (orange wires).
°F
Room
A ir
Ω
Indoor
Coil
Ω
3800 Series
Outdoor Coil
Ω
Outdoor Air
Ω
10 63260 94900 28030
30 34620 51940 15340
32 32890 49330 14570
50 19970 29960 8850
70 11950 17930 5300
90 7320 10970 3280
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