16
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:
In cooling if the outdoor air sensor indicates ≥ 10F
warmer than the coil sensor (or) the outdoor air sensor
indicates ≥ 20F cooler than the coil sensor, the sensors
are out of range.
In heating if the outdoor air sensor indicates ≥ 35F
warmer than the coil sensor (or) the outdoor air sensor
indicates ≥ 10F 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 7.
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 7 gives possible causes and actions
related to each error.
OAT Thermistor must be locked in
place with spherical nib end facing to-
wards the front of the control box
Fig. 10 − Outdoor Air Thermistor (OAT) Attachment
OCT Thermistor
must be secured
tight on stub tube.
Fig. 11 − Outdoor Coil Thermistor (OCT) Attachment
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