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THERMISTOR CURVE
90
80
70
60
50
40
30
20
10
0
0
20
40
(-17.77)
(-6.67)
(4.44)
TEMPERATURE °F (°C)
Fig. 7 - - Resistance Values Versus Temperature
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code. (See Table 6.)
IMPORTANT: The outdoor air thermistor and coil thermistor
should be factory mounted in the final locations. Check to ensure
thermistors are mounted properly per Fig. 8 and Fig. 9.
OAT Thermistor must be locked in
place with spherical nib end facing to-
wards the front of the control box
Fig. 8 - - Outdoor Air Thermistor (OAT) Attachment
Winding
Start (S- -C)
Run (R- -C)
Winding
Start (S- -C)
Run (R- -C)
60
80
100
120
(15.56)
(26.67)
(37.78)
(48.89)
A08054
Table 5 – Two- -Stage Compressor Resistances
(Winding Resistance at 70_F±20_F / 21_C±11_C)
286A024
2.74
0.80
288A024
1.40
1.32
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor air
temperature sensor and outdoor coil temperature sensor to ensure
proper operating conditions. The comparison is:
S In cooling if the outdoor air sensor indicates ≥ 10_F
(≥ 5.6_C) warmer than the coil sensor (or) the outdoor air
sensor indicates ≥ 20_F (≥ 11_C) cooler than the coil sensor,
the sensors are out of range.
S In heating if the outdoor air sensor indicates ≥ 35_F (≥
19.4_C) warmer than the coil sensor (or) the outdoor air
sensor indicates ≥ 10_F (≥ 5.6_C) cooler than the coil sensor,
the sensors are out of range.
If the sensors are out of range, the control will flash the appropriate
fault code as shown in Table 6.
The thermistor comparison is not performed during low ambient
cooling or defrost operation.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of
outdoor air thermistor (OAT) and/or outdoor coil thermistor
(OCT).
If the OAT sensor should fail, low ambient cooling will not be
allowed and the one- -minute outdoor fan off delay will not occur.
Defrost will be initiated based on coil temperature and time.
If the OCT sensor should fail, low ambient cooling will not be
allowed. Defrost will occur at each time interval during heating
operation, but will terminate after 5 minutes.
If there is a thermistor out of range error, defrost will occur at each
time interval during heating operation, but will terminate after 5
minutes.
Count the number of short and long flashes to determine the
appropriate flash code. Table 6 gives possible causes and actions
related to each error.
Fig. 9 - - Outdoor Coil Thermistor (OCT) Attachment
286A036
286A048
1.98
0.75
288A036
288A048
1.29
0.89
13
OCT Thermistor
must be secured
tight on stub tube.
286A060
1.55
0.74
0.48
0.36
288A060
1.52
0.60
0.64
0.49
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