Daikin FDMQ09RVJU, Manual

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Troubleshooting SiUS071735EB
75 Service Diagnosis
4.11 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 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