Fault phenomenon: TOYOTA air conditioning system manual air-conditioning system in summer air conditioning refrigeration effect is bad, air conditioning compressor stop work. The cause of the failure: 1. when the evaporation chamber of the cab is about to freeze, the evaporative box temperature sensor tells the air conditioner ECU that the evaporator will freeze at this time, and the compressor needs to be stopped to prevent the freezing of the evaporation tank. 2. when the leakage of the air conditioning pipeline makes the system R134a too low (low pressure) or overcharge R134a to overcharge the system, the air conditioning high / low voltage switch cuts off the signal to the air conditioning ECU. When the air conditioning ECU does not receive the signal, it cuts off the electromagnetic clutch circuit of the air conditioner compressor, so that the electromagnetic clutch stops working to prevent more serious damage. The solution is to re exhaust, leak and charge R134a for the refrigeration system. If the evaporating box is frozen, the air conditioning unit is replaced.