Troubleshooting
SiBE041010EA
57
Service Diagnosis
4.6
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
running 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 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.
Input current × input voltage
≤
A
× output fre
B
Output frequency >
C
Refrigerant shortage detection II:
The following conditions continue for 80 seconds.
Opening of the electronic expansion valve
≥
D
Discharge pipe temperature >
E
× target discharge pipe tempe
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 electronic expansion valve
A
(–)
B
(W)
C
(Hz)
20/25 class
828/256
–10
50
35 class
777/256
–15
50
D
(pulse)
E
(–)
F
(°C)
20/25 class
Cooling
470
190/128
–7
Heating
211/128
–11
35 class
Cooling
470
160/128
–1.5
Heating
172/128
–8
