SiUS04-904 Troubleshooting
140 Service Diagnosis
4.21.2 15/18/24 Class
Remote
Controller
Display
U0
Method of
Malfunction
Detection
Refrigerant shortage detection I :
Refrigerant shortage is detected by checking the CT-detected input current value and the
compressor running frequency.
Refrigerant shortage detection II:
Refrigerant shortage is detected by checking the discharge pipe temperature and the opening of
the electronic expansion valve. If the refrigerant is short, the discharge pipe temperature tends to
rise.
Refrigerant shortage detection III:
Refrigerant shortage is detected by checking the difference between air suction and discharge
temperature.
Malfunction
Decision
Conditions
Refrigerant shortage detection I :
Input current < (A/Hz) x Compressor running frequency Voltage +
However, when the status of running frequency > 55 (Hz) is kept on for a certain time.
Note : The values are different from model to model.
If refrigerant shortage error takes place 4 times successively, the system is shut down. The error
counter is reset if this or any other error does not occur during the following 60-minute compressor
running time (total time).
Supposed
Causes
Refrigerant shortage (refrigerant leakage)
Poor compression performance of compressor
Discharge pipe thermistor disconnected, or indoor unit or outdoor unit heat exchanger
thermistor disconnected, room or outside air temperature thermistor disconnected
Stop valve closed
Electronic expansion valve defective
1756 / 256 –50
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