A Beiqi Luling pickup coach car was suddenly burnt down in the summer training. In order not to affect the training of the vehicle, 1 new electromagnetic clutch coils were replaced during maintenance. But after 1 weeks, the coil of the electromagnetic clutch was burned again. Diagnosis analysis: the cause of the electromagnetic clutch coil in the air conditioning system is burned out, except for the quality problem, the main reason is that the pressure of the air conditioning system is too high, and the resistance of the compressor is too high, which exceeds the electromagnetic suction of the electromagnetic clutch coil, so that the main and passive disc of the clutch is caused by sliding friction and causing overheating to burn down. There are 3 reasons why the pressure of the air conditioning system is too high: 1) stop the engine to operate at idle speed, and use air conditioning for a long time in the sun; 2) when the radiator fan fails, the air conditioner is used for a long time and high intensity (the radiator fan and the air-conditioner fan are used together); 3) the added R13 in the refrigeration system Idle running 4A overdose.