Troubleshooting SiMT041509E
61 Service Diagnosis
4.7 Signal Transmission Error (Between Indoor Unit and
Outdoor Unit)
Error Code
U4
Method of Error
Detection
The data received from the outdoor unit in signal transmission is checked whether it is normal.
Error Decision
Conditions
The data sent from the outdoor unit cannot be received normally, or the content of the data is
abnormal.
Supposed
Causes
Power supply voltage is not as specified.
Reduction of power supply voltage
Wiring error
Breaking of the connecting wires between the indoor and outdoor units (wire No. 3)
Defective outdoor unit PCB
Short circuit inside the fan motor winding
Defective indoor unit PCB
Disturbed power supply waveform
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