SiUS041829E Troubleshooting
Part 6 Service Diagnosis 81
4.8 Signal Transmission Error (Between Indoor Unit and
Outdoor Unit)
Error Code U4
Method of Error
Detection
The signal transmission data received from the outdoor unit 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 out of specification
Reduction of power supply voltage
Wiring error
Breaking of the connection 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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