SiBE121123_A Troubleshooting for Outdoor Unit
Service Diagnosis 182
7.3 Outdoor Unit PCB Abnormality or Signal Transmission
Error
Error Code
U4
Method of Error
Detection
Detection within the program of the microcomputer that the program is in good running order.
Error Decision
Conditions
The program of the microcomputer does not work in order.
Signal transmission between the units cannot be performed for more than 15 seconds.
Zero-cross signal cannot be detected for more than 10 seconds.
Supposed
Causes
Display disabled due to power supply fault
Momentary fall of voltage
Momentary power failure
Defective varistor
Defective fuse
Defective thermal fuse on outdoor terminal board
Defective terminal board
Defective outdoor unit PCB
Improper grounding work
Noise
Defective fan motor
Improper wiring between indoor and outdoor units
Defective indoor unit PCB
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