SiUS04-904 Troubleshooting
138 Service Diagnosis
4.21 Refrigerant Shortage
4.21.1 09/12 Class
Remote
Controller
Display
U0
Method of
Malfunction
Detection
Refrigerant shortage detection I :
Refrigerant shortage is detected by checking 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 > (Hz) is kept on for a certain time.
Note : The values are different from model to model.
Refrigerant shortage detection III :
When the difference of the temperature is smaller than , it is regarded as refrigerant shortage.
If a 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 outdoor air temperature thermistor disconnected
Stop valve closed
Electronic expansion valve defective
640 / 256 0 55
Cooling
room temperature – indoor heat exchanger temperature 7.2°F
outdoor heat exchanger temperature – outdoor temperature 7.2°F
Heating
indoor heat exchanger temperature – room temperature 7.2°F
outdoor temperature – outdoor heat exchanger temperature
5.4°F
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