Specifications

SiBE04-624_B Troubleshooting
Service Diagnosis 101
2.18 Outdoor Unit PCB Abnormality or Communication
Circuit Abnormality
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
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The program of the microcomputer does not work in order.
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Signal transmission between the units cannot be performed for more than 15 seconds.
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Zero-cross signal cannot be detected for more than 10 seconds.
Supposed
Causes
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Display disabled due to power supply fault
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Momentary fall of voltage
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Momentary power failure
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Defective varistor
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Defective fuse
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Defective thermal fuse on outdoor terminal board
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Defective terminal board
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Defective outdoor unit PCB
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Improper grounding work
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Noise
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Defective fan motor
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Improper wiring between indoor and outdoor units
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Defective indoor unit PCB