Panasonic WH-UD28AE Service Manual page 60

16.5.18. Power Factor Correction (PFC) Abnormality (F90)
Malfunction Decision Conditions:
During operation of heating, PFC protection circuitry at the outdoor unit main PCB senses abnormal high DC voltage level.
Malfunction Caused:
1. DC voltage peak due to power supply surge.
2. DC voltage peak due to compressor windings not uniform.
3. Faulty outdoor unit PCB.
Abnormality Judgment:
Continue 4 times in 10 minutes.
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