Troubleshooting - Panasonic CS-E18NKUA Service Manual

15.4.20 F99 (Output Over Current Detection)
Malfunction Decision Conditions
During operation of cooling and heating, when an output over-current (18.5A) is detected by checking the current that
flows in the inverter DC peak sensing circuitry.
Malfunction Caused
DC peak due to compressor failure.
DC peak due to defective power transistor(s).
DC peak due to defective outdoor unit PCB.

Troubleshooting

Checking the power transistor
Never touch any live parts for at least 10 minutes after turning off the circuit breaker.
If unavoidable necessary to touch a live part, make sure the power transistor's supply voltage is below 50V using
the tester.
For the UVW, make measurement at the Faston terminal on the board of the relay connector.
Tester's negative terminal
Tester's positive terminal
Normal resistance
Abnormal resistance
Power transistor (+)
UVW Power transistor (+)
66
UVW Power transistor (-)
UVW
Several kΩ to several MΩ
0 or ∞
UVW
Power transistor (-)