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13.4.26 F99 (Output Over Current Detection)
Malfunction Decision Conditions
During operation of cooling, 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
Power transistor (+)
UVW
Power transistor (-)
UVW
Tester’s positive terminal
UVW
Power transistor (+)
UVW
Power transistor (-)
Normal resistance
Several kΩ to several MΩ
Abnormal resistance
0 or ∞
For safety reason and to prevent component
breakdown, always switch off the power
before remove and connect the component.
Replace the outdoor unit PCB.
Compressor defective due to winding
shorted.
Replace compressor.
Outdoor electronic circuit defect due to
power transistor short.
Replace the outdoor unit PCB.
When F99 indication happens.
Get restarted and measure the input
current.
Are the compressor’s winding resistance
(U-V, V-W or U-W) shorted?
Input current > 18.5A?
NO
Turn off the power and disconnect
the harnesses U, V and W.
Measure the winding resistance
between U-V, V-W and W-U.
Check the compressor winding resistance:
NO
YES
YES
Caution
