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Outdoor Air Thermistor
The outdoor air thermistor is located on the top
left side of the outdoor coil. This thermistor
measures the outside ambient temperature.
Outdoor Air Thermistor Diagnosing
If an outdoor air 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 Air Thermistor Operation
Enter Service Mode by pressing and holding
+
and
-
buttons. On entry, the display lights all
LED's. Press
MODE
until
S3
is shown in the
display. Pressing
+
displays the indoor coil
temperature.
AUX
key exits Service Mode.
Verify Outdoor Air Thermistor Resistance
Value
Outdoor air thermistor resistance values can be
checked from the main control board at the J503
connector.
• Pin 1 (
red
) to pin 2 (
red
): Use Outdoor Air
Thermistor Resistance chart below to verify
resistance to actual temperature.
Outdoor Air Thermistor
Resistance (ohms)
°F
Air
10
28030
30
15340
32
14570
50
8850
70
5300
90
3280
Outdoor Air Thermistor Removal
1. Remove junction box cover and main control
board cover.
2. Remove one 5/16-in. screw from fan shroud.
Outdoor Air
Thermistor
5/16" Screw
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.
Zip tie
