Troubleshooting SiMT041509E
59 Service Diagnosis
4.6 Low-voltage Detection or Over-voltage Detection
Error Code
U2
Method of Error
Detection
Indoor Unit
The zero-cross detection of the power supply is evaluated by the indoor unit PCB.
Outdoor Unit
Low-voltage detection:
An abnormal voltage drop is detected by the DC voltage detection circuit.
Over-voltage detection:
An abnormal voltage rise is detected by the over-voltage detection circuit.
Error Decision
Conditions
Indoor Unit
There is no zero-cross detection in approximately 10 seconds.
Outdoor Unit
Low-voltage detection:
The voltage detected by the DC voltage detection circuit is below 196 V.
The compressor stops if the error occurs, and restarts automatically after 3-minute standby.
Over-voltage detection:
An over-voltage signal is fed from the over-voltage detection circuit to the microcomputer
(over 480 V).
The compressor stops if the error occurs, and restarts automatically after 3-minute standby.
Supposed
Causes
Power supply voltage is not as specified.
Defective DC voltage detection circuit
Defective over-voltage detection circuit
Defective PAM control part
Disconnection of compressor harness
Short circuit inside the fan motor winding
Noise
Momentary drop of voltage
Momentary power failure
Defective outdoor unit PCB
Defective indoor unit PCB
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