Service Manual
47
After a 15 minute delay, if there is still a call for cooling, the
compressor contactor is energized. If the thermal protector
has not re- set, the outdoor fan is turned off. If the call for
cooling continues, the control will energize the compressor
contactor every 15 minutes. If the thermal protector closes,
(at the next 15 minute interval check), the unit will resume
operation.
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 13) 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. 34 for
resistance values versus temperature.
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code. (See table 13).
IMPORTANT: The outdoor air thermistor and coil thermistor
are factory mounted in the correct locations. Do not
re- locate thermistor sensors.
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
outdoor 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 13).
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 Figure 34 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 12 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. Time 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 13 gives possible causes and
actions related to each error.
Example: 3 short flashes followed by 2 long flashes
indicates a 32 code. Table 13 shows this to be low pressure
switch open.