Carrier 40MB C Series Service Manual page 30

Inverter compressor drive error diagnosis and solution (P4)
Error Code
Malfunction decision conditions
Supposed causes
Main Parts Check
Temperature sensor checking
Disconnect the temperature sensor from PCB, measure the resistance value with a tester.
Temperature Sensors.
Room temp.(T1) sensor,
Indoor coil temp.(T2) sensor,
Outdoor coil temp.(T3) sensor,
Outdoor ambient temp.(T4) sensor,
Compressor discharge temp.(T5) sensor.
Measure the resistance value of each winding by using the multi−meter.
P4
An abnormal inverter compressor drive is detected by a special detection circuit,
including communication signal detection, voltage detection, compressor rotation speed
signal detection.
S
Wiring mistake; IPM malfunction; outdoor fan ass'y faulty
S
Compressor malfunction; Outdoor PCB faulty
Fig. 40 – Troubleshooting
Fig. 41 – Tester
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