Troubleshooting SiBE05-722EE
70 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.
Refrigerant shortage detection III:
Refrigerant shortage is detected by checking the difference between suction and discharge
temperature.
Error Decision
Conditions
Refrigerant shortage detection I:
The following conditions continue for 7 minutes.
Input current × input voltage
≤
A × output frequency + 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 temperature + F
Refrigerant shortage detection III:
When the difference of the temperature is smaller than G°C, it is regarded as refrigerant
shortage.
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 (coefficient) B (W) C (Hz)
640/256 0 55
D (pulse) E (constant) F (°C)
RK(X)S25/35E2V1B 480 255/256 30
RK(X)S25/35G2V1B
RK(X)S25/35G2V1B9
RXS25/35J2V1B
RXS25K3V1B
RXS35K2V1B
RXS25/35L2V1B
RXS25/35L3V1B
480 128/128 30
Operation
mode
Description G (°C)
Cooling
room thermistor temperature – indoor heat exchanger temperature 4.0
outdoor heat exchanger temperature – outdoor temperature 4.0
Heating
indoor heat exchanger temperature – room thermistor temperature 3.0
outdoor temperature – outdoor heat exchanger temperature 3.0
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