SiBE121123_A Troubleshooting for Outdoor Unit
Service Diagnosis 178
7. Troubleshooting for Outdoor Unit
7.1 Refrigerant Shortage
Error Code
U0
Method of Error
Detection
Refrigerant shortage detection I :
Refrigerant shortage is detected by checking the input current value and the compressor output
frequency. If the refrigerant is short, the input current is lower than the normal value.
Refrigerant shortage detection II :
Refrigerant shortage is detected by checking the discharge pipe temperature and the opening of
the outdoor electronic expansion valve. If the refrigerant is short, the discharge pipe
temperature tends to rise.
Error Decision
Conditions
Refrigerant shortage detection I :
The following conditions continue for 7 minutes.
DC current × DC voltage ≤ A × Compressor output frequency + B
Output frequency > C
Refrigerant shortage detection II :
The following conditions continue for 80 seconds.
Opening of the outdoor electronic expansion valve ≥ D
Discharge pipe temperature > E × target discharge pipe temperature + F
If the error repeats, the system is shut down.
Reset condition: Continuous run for about 60 minutes without any other error
Supposed
Causes
Disconnection of the discharge pipe thermistor, indoor or outdoor heat exchanger thermistor,
room or outdoor temperature thermistor
Closed stop valve
Refrigerant shortage (refrigerant leakage)
Poor compression performance of compressor
Defective outdoor electronic expansion valve
A
(–)
B
(W)
C
(Hz)
40 class 2111/256 –361 51
50 class 4628/256 –608 48
D
(pulse)
E
(–)
F
(°C)
450 255/256 20
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