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Shanghai Volkswagen Santana 3000 Zhijun car with a mileage of over 200 thousand km. Users reflect: the car's air conditioning is not cool. Fault diagnosis: 1) when the fault is verified, it is found that the air outlet in the middle is not cool. The air outlet temperature of the air conditioner is measured at 15 degrees centigrade with a thermometer, which is higher than the normal vehicle temperature. 2) check the compressor, the compressor is normal, and the high and low pressure are normal, the refrigeration is normal. 3) self diagnosis: (1) switch on the ignition switch; second, press "MODE" and hold it, then press "9" to maintain 3S and enter the self diagnostic mode. The fault code is 02 inner loop valve motor. 4) according to the indication of the fault code, the internal circulation valve motor and the inner circulation valve are checked. It is found that the inner circulation air valve is always in the open state, whether it is the open loop or the outside circulation. It can be preliminarily judged that the fault is due to the fact that the inner circulation air door can not be shut down, and that fresh air enters too many air channels, resulting in insufficient intensity of air conditioning and refrigeration. According to this, the fault source can be preliminarily determined: (1) internal circulation motor failure or internal circulation valve stagnation; (2) air conditioning panel failure; (3) the circuit fault between the internal circulation motor and the air conditioning panel. In accordance with the principle of easy to difficult, check the following steps: first, remove the inner circulating air door motor (V154) to check the damper. The inner circulating air door is pulled, and the inner circulating air door is free of movement. Replacement of the valve motor, the failure is still. Replace the air conditioning control panel, the failure is still. Next, check the circuit between the inner circulating air door motor and the air conditioner panel, as shown in Figure 1. Analysis of the circuit diagram shows that the purple brown line (T6t/1) is the V154 power supply for the inner circulating air door motor. Huang Bai line (T6t/6) is the inner circulating air door motor wire. T6T/5 is the G143 of the throttle motor potentiometer, the T6T/4 is the input line of the throttle motor potentiometer G143, and the T6T/2 is the output adjustment signal line. When the air conditioning works, the purple white line is fed by the air conditioning relay to the power supply voltage, and the circuit is formed through the blue and black line to the J127 iron lap, and the J127 brown and black line foot (T32E/6) is the control signal of the J127 output control end. Open the internal circulation switch, the purple white line provides the power supply voltage, the brown black line output adjustment signal, according to the potentiometer G143 signal (internal circulation valve condition), to adjust. Use multimeter to check, turn on the ignition switch, the purple brown line (T6t/1) voltage is 125V, no short circuit. Purple yellow line (T6t/5) voltage is 5V, no short-circuit phenomenon. The purple white line T6t/3 is normal. Disconnect the 32 pin plug of the air conditioner panel and check the blue white line (T6d4) to the black line (T32E/10) with a multimeter. The resistance value is 0.5 ohm, and there is no short-circuit phenomenon. Check the T6t/6 to T32E/22 blue black line again, the resistance value is 0.5 ohms. Check whether there is a short circuit phenomenon, the foot T6t/6 to ground resistance value of 3 Omega, this resistance is abnormal, the foot T6t/2 to ground resistance value of 35 Omega, this resistance is not normal, under normal conditions should be infinite. Then the circuit began to be checked and the central relay was removed, and the T6 "to" 2E/22 blue black line and the T6t/2 to T32E/6 Brown / black line had been worn out, and the ground short circuit state was formed. When the internal circulation switch was opened, the inner circulation motor could not be adjusted and was in a constant state, so that the cooling of the air conditioning was insufficient. After the repair of the wire harness, the inner loop air door can be operated normally, and the outlet temperature reaches 6 degrees.