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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. 8 for resistance values versus temperature. If the
outdoor ambient or coil thermistor should fail, the control will
flash the appropriate fault code (see Table 6.)
IMPORTANT: Outdoor air thermistor and coil thermistor are
factory mounted in the final locations. Check to insure thermistors
are mounted properly per Fig. 9 and Fig. 10.
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:
— If the outdoor air sensor indicates 10_F (5.56_C) warmer
than the coil sensor (or) the outdoor air sensor indicates
20_F (11.11_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.
OAT Thermistor must be
locked in place with spheri-
cal nib end facing towards
the front of the control box
Fig. 9 - - Outdoor Air Thermistor (OAT) Attachment
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. 8 - - Resistance Values Versus Temperature
NO
USE
A12263
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 control box
Status Codes
Table 6 shows the status codes flashed by the amber status light.
Most system problems can be diagnosed by reading the status code
as flashed by the amber status light on the control board.
The codes are flashed by a series of short and long flashes of the
status light. The short flashes indicate the first digit in the status
code, followed by long flashes indicating the second digit of the
error code.
The short flash is 0.25 seconds ON and the long flash is 1.0 second
ON. Time between flashes is 0.25 seconds. Time between short
flash and first long flash is 1.0 second.
repeating is 2.5 seconds with LED OFF.
EXAMPLE:
3 short flashes followed by 2 long flashes indicates a 32 code.
Table 6 shows this to be low pressure switch open.
60
80
100
120
(15.56)
(26.67)
(37.78)
(48.89)
OCT Thermistor must be
secured tight on the liquid tube.
Fig. 10 - - Outdoor Coil Thermistor (OCT) Attachment
11
Time between code
A08054
A11143
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