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Outdoor Coil Thermistor
The outdoor coil thermistor is located on the
top left side of the outdoor coil. This thermistor
measures the outdoor coil temperature.
Outdoor Air Thermistor Diagnosing
If an outdoor coil thermistor were to fail, the
resistance heater and fan will continue to operate,
but the compressor will not come on for cooling or
heat pump.
Check for Fault Codes
Check fault codes by pressing and holding MODE
and then press AUX. Verify whether fault 5
(Outside Thermistor Fault) code is active. Record
any other faults and clear the codes by pressing
AUX.
Verify Outdoor Coil Thermistor Operation
Enter Service Mode by pressing and holding +
and - buttons. On entry, the display lights all
LED's. Press MODE until S4 is shown in the
display. Pressing + displays the indoor coil
temperature. AUX key exits Service Mode.
Verify Outdoor Coil Thermistor Resistance
Value
Outdoor coil thermistor resistance values can be
checked from the main control board at the J503
connector.
• Pin 4 (red) to pin 5 (red): Use Outdoor Coil
Thermistor Resistance chart below to verify
resistance to actual temperature.
Outdoor Coil Thermistor
Resistance (ohms)
°F
10
30
32
50
70
90
Air
28030
15340
14570
8850
5300
3280
Outdoor Air Thermistor Removal
1. Remove junction box cover and main control
board cover.
Outdoor Coil
Thermistor
2. Remove one 5/16-in. screw from fan shroud.
3. Clip zip tie holding the thermistor harness
to the tubing. NOTE: Install a new zip tie to
the tubing and harness after replacing the
thermistor.
– 33 –
5/16" Screw
Zip Tie
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