14
TEMPERATURE THERMISTORS
Thermistors are electronic devices which sense temperature. As
the temperature increases, the resistance decreases. Thermistors
are used to sense outdoor ambient (OAT) and coil temperature
(OCT). Refer to Fig. 9 for resistance values versus temperature.
If the outdoor ambient or coil thermistor should fail, the control
will flash the appropriate fault code (see Table 5.)
IMPORTANT
: Outdoor air thermistor and coil thermistor are
factory mounted in the final locations.
Check to insure
thermistors are mounted properly per Fig. 11 and Fig. 12.
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
If the outdoor air sensor indicates
≥
10
_
F warmer than the
coil sensor (or) the outdoor air sensor indicates
≥
20
_
F
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 5.
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 and/or coil thermistor.
If the OAT sensor should fail, low ambient cooling will not be
allowed and the one--minute outdoor fan off delay will not occur.
If the OCT sensor should fail, low ambient cooling will not be
allowed.
OAT Thermistor must be
locked in place
with spherical nib end facing
towards the front of the con-
trol box
Fig. 11
---
Outdoor Air Thermistor (OAT) Attachment
OCT Thermistor must be
secured tight on the liquid
tube.
Fig. 12
---
Outdoor Coil Thermistor (OCT) Attachment
24AN
A