Shanghai Volkswagen Passat runs a 1.8T car with a mileage of about 100 thousand km. When the vehicle turns on the air conditioner, the 2 electronic fans can operate normally, but the air conditioning compressor does not work. After taking the car: first, verify the failure phenomenon. After starting the engine, connect the air conditioner (A/C) switch and the blower switch, the indicator light on the air conditioner switch on, the blower running, the wind blower blowing out, the electronic fan on both sides of the left and right, but touch the throttle valve of the air conditioning high pressure pipe, not cool, check the electromagnetic clutch of air compressor, and do not absorb, It shows that the air conditioner compressor is not working. Then use multimeter to measure the power supply of the electromagnetic clutch of the air conditioning compressor, normal. Connect the air conditioning manifold pressure gauge group to observe the pressure in the high and low pressure system of the air conditioner. Through the measurement, it is found that the refrigerant quantity in the air conditioning system is normal. Connect VAS5051 into 01-08-050, the third area of this group of data is air conditioning A/C switch signal, VAS5051 shows "ON", indicating that the air conditioner has been connected, but the air conditioner compressor signal in the fourth area is "OFF", indicating that the air conditioner compressor is not connected. From these two data, the air conditioning signal has been conveyed to the engine ECU, but the ECU does not deliver the signal to the air conditioner compressor, and then the inspection focus is turned to the engine control system. The fault storage of the engine system is detected, a fault code on the voltage of the air flow sensor is transferred, and then the 01-08-002 data block is read. The result shows that the air flow sensor signal in the fourth zone is 0.00g/s. In order to quickly determine whether the air flow sensor is a problem, a new air flow sensor was replaced, but the replacement test found that the failure was still. Then the circuit diagram of the car is found. The circuit diagram is used to check the connector terminals of the air flow sensor, and the result shows that the position of the terminal 4 and terminal 5 of the air flow sensor is wrong. Troubleshooting: swap the location of the wrong air flow sensor wire connector terminal 4 and terminal 5.