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If the thermal cutout trips for three consecutive cycles, then unit
operation is locked out for 4 hours and the appropriate fault code
(See Table 4) is displayed.
Contactor Shorted Detection
If there is compressor voltage sensed when there is no demand for
compressor operation, the contactor may be stuck closed. The
control will flash the appropriate fault code. Check the contactor
and control box wiring.
No 230V at Compressor
If the compressor voltage is not sensed when the compressor
should be starting, The contactor may be stuck open or the unit
disconnect or circuit breaker may be open. The control will flash
the appropriate fault code. Check the contactor, unit disconnect or
circuit breaker and control box wiring.
Temperature Thermistors
Thermistors are electronic devices which sense temperature. As the
temperature increases, the resistance decreases. Thermistors are
used to sense outdoor air (OAT) and coil temperature (OCT).
Refer to Fig. 15 for resistance values versus temperature.
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code. (See Table 4)
IMPORTANT: The outdoor air thermistor and coil thermistor are
factory mounted in the correct locations. Do not re–locate thermistor
sensors.
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. 15 --- Resistance vs. Temperature Chart
60
80
100
120
(15.56)
(26.67)
(37.78)
(48.89)
A08054
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/–12.22_C warmer than the coil sensor (or) the out-
door air sensor indicates 20_F/–6.67_C cooler than the
coil sensor, the sensors are out of range.
S
In heating if the outdoor air sensor indicates 35_F/1.67_C
warmer than the coil sensor (or) the outdoor air sensor
indicates 10_F/–12.22_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. (See Table 4)
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.
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.
Thermistor Curve: The resistance vs. temperature chart shown in
Fig. 14 enables the technician to check the outdoor air and outdoor
coil thermistors for proper resistance. Unplug the thermistor
assembly from the circuit board and measure resistance across each
thermistor. For example, if the outdoor temperature is
60_F/15.56_C, the resistance reading across the outdoor air
thermistor should be around 16,000 Ohms.
Status Codes
Table 4 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 second ON and the long flash is
1.0 second ON. Time between flashes is 0.25 second. Time
between short flash and first long flash is 1.0 second.
between code repeating is 2.5 seconds with LED OFF.
Count the number of short and long flashes to determine the
appropriate flash code. Table 4 gives possible causes and actions
related to each error.
Example: 3 short flashes followed by 2 long flashes indicates a 32
code. Table 4 shows this to be low pressure switch open.
12
Time
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