Daikin FTX-N Series, Service Manual

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SiUS091601EA Troubleshooting for FDMQ Series
Part 6 Service Diagnosis 146
6.8 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 150 ~ 200 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 out of specification
 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