Daikin FTXM-V Series, Service Manual

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SiUS042113E Troubleshooting
Part 6 Service Diagnosis 99
4.8 Low-voltage Detection or Over-voltage Detection
Error Code
U2
Method of Error
Detection  Indoor Unit
Low-voltage detection:
An abnormal voltage drop is detected by the DC voltage detection circuit.
 Outdoor Unit
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

Indoor Unit
The voltage detected by the DC voltage detection circuit is below 140 V.
 Outdoor Unit
Low-voltage detection:
 The voltage detected by the DC voltage detection circuit is below 162 V (09/12 class), 160 V
(18/24 class).
 The compressor stops if the error occurs, and restarts automatically after 3-minute standby.
Over-voltage detection:
 The voltage detected by the DC voltage detection circuit is below 458 V (depending on the
model).
 An over-voltage signal is fed from the over-voltage detection circuit to the microcomputer.
 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
 Defective indoor unit PCB