Repair Method: Replace with the same model D3.
Fault Symptoms: Initially, no cooling occurred, the yellow light lit up, and the AC contactor kept burning out. This issue was reported by Beijing Zhigao Air Conditioning Repair Center regarding Zhigao split-type air conditioners that repeatedly burned out AC contactors.
Analysis and Maintenance: After replacing the AC contactor, upon turning on the machine, measurements of the three-phase four-wire voltage inside the unit and the control transformer's output of AC 12V, 6.3V, 12.3V, as well as DC voltages of 9V and 6V, were all normal. No abnormalities were detected during startup; the three-phase current of the compressor was balanced, and cooling functioned properly. However, after two days of normal operation, the fault reoccurred, indicating a problem with circuit components. Upon inspection, it was found that the rectifier diodes D1-D4 (IN4003) in the over/under-voltage protection circuit had poor thermal stability, particularly D3, which led to instability in the DC voltage.
Source of Information: Zhigao Air Conditioner Repair http://blog.163.com/zhigao_kt120/.