A Changan Mazda 32. 0L AT car with a mileage of about 18 thousand km. The owner reflected that when the vehicle was running for a period of time, the air conditioner was not refrigerant and the wind was blowing at room temperature. Failure does not happen frequently. It usually happens once in a few days. After receiving the car: routine examination of the car, no abnormalities were found. Many road tests are carried out, and the failure phenomenon is finally reproduced. According to the failure phenomenon, through careful thinking and analysis, judging the failure may be caused by the following aspects: cooling fan intermittently stop work, causing compressor stop or condenser heat dissipation; the intermittency of the thermostat can not be opened, the temperature of the coolant is too high to stop the compressor; the air conditioning circuit control system malfunction or The internal temperature of the engine control unit PCM is too high.