Daikin FTX20K2V1B, Service Manual

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Troubleshooting SiBE041525F
55 Service Diagnosis
4.6 Low-voltage Detection or Over-voltage Detection
Error Code
U2
Method of Error
Detection Low-voltage detection:
An abnormal voltage drop is detected by the DC voltage detection circuit.
Over-voltage detection:
An abnormal voltage rise is detected by the over-voltage detection circuit.
Error Decision
Conditions Low-voltage detection:
 The voltage detected by the DC voltage detection circuit is below 180 ~ 196 V (depending on
the model).

The compressor stops if the error occurs, and restarts automatically after 3-minute standby.
Over-voltage detection:
 An over-voltage signal is fed from the over-voltage detection circuit to the microcomputer
(over 458 ~ 500 V, depending on the model).

The compressor stops if the error occurs, and restarts automatically after 3-minute standby.
Supposed
Causes

Power supply voltage is not as specified.
 Defective DC voltage detection circuit
 Defective over-voltage detection circuit

Defective PAM control part

Disconnection of compressor harness
 Short circuit inside the fan motor winding
 Noise

Momentary drop of voltage

Momentary power failure
 Defective outdoor unit PCB