Service Manual

SiUS041638E Troubleshooting
Service Diagnosis 66
4.7 Signal Transmission Error (between Indoor Unit and
Outdoor Unit)
Error Code
U4
Method of Error
Detection
The signal transmission data 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 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