Mitsubishi Electric U9

Critical

PUY-P42, 48, 125VKA.TH / PUY-M125VKA-SG — Abnormality of voltage (overvoltage or undervoltage)

Mitsubishi Electric U9: Abnormality of voltage (overvoltage or undervoltage) This fault typically halts operation and needs immediate attention.

Possible causes

Compressor wiring loose, disconnected, or wrongly connected
Power supply voltage drops below the rated value

Check steps

Measure resistance values among terminals on the compressor with a tester
Check power supply voltage and the wiring of CN52C

Affected parts

Compressor
CN52C connector
Power supply wiring

Safety note

High-voltage hazard — disconnect power and discharge capacitors before working on the compressor circuit.

Source: Mitsubishi Electric resmi servis kilavuzu (bagimsiz cift-dogrulandi) — Mitsubishi Electric Mr. SLIM Outdoor Unit (PUY-P42,48,125VKA.TH series) Service Manual — Error Code U9: "Abnormality of voltage" (overvoltage or voltage shortage / abnormal synchronous signal to main circuit / current sensor error), listed as check-code No.14 in the Mr. SLIM error priority list. Troubleshooting inclu…

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