Troubleshooting SiMT041509E59 Service Diagnosis4.6 Low-voltage Detection or Over-voltage DetectionError Code U2Method of ErrorDetection+ Indoor UnitThe zero-cross detection of the power supply is evaluated by the indoor unit PCB.+ Outdoor UnitLow-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 DecisionConditions+ Indoor UnitThere is no zero-cross detection in approximately 10 seconds.+ Outdoor UnitLow-voltage detection: The voltage detected by the DC voltage detection circuit is below 196 V. 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 480 V). The compressor stops if the error occurs, and restarts automatically after 3-minute standby.SupposedCauses 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 Defective indoor unit PCB
