Failure symptoms: automatic air conditioning air volume adjustment failure.
    Troubleshooting: This car automatic air conditioning air volume options, whether it is automatic or manual, from low to high divided into six files. First, confirm the fault symptoms, the automatic, manual switch to AUTO (automatic) position, according to the temperature set value of air conditioning air volume from weak to strong continuous change, but switch to manual position, even if the temperature is set low, air volume is not stable , Occasionally large air volume; temperature set high, the amount of air volume change is not large. This means that the manual can not be the amount of air from the trace to the amount of high adjustment.
    In the manual position to set the temperature is high, or in the automatic position on the temperature set to the lowest, you can clearly hear the action of the relay sound and blower sound, it should be said that the power supply and motor are no problem. Blower motor mounted with a three-pin connector, about the power transistor, two thick lines is the power cord, a thin line is the control line.
    In the automatic state to change the set temperature, to confirm the control line voltage, the voltage does change with the set temperature, but the wind with the voltage changes, so the power transistor is normal. In the manual state, adjust the fan switch from the LO (low temperature) position to the HI (high temperature) position, the voltage change is unstable, and the corresponding air volume change is unstable. The principle is that when the fan switch is operated, the base current of the power transistor is divided into six levels, so that the collector and emitter voltages of the power transistor are also divided into six levels, so that the voltage applied to the blower motor is also divided into six levels , So there are six levels of air volume.
    When the air conditioner is in the automatic adjustment state, the fan motor voltage can change continuously, so the automatic air conditioning amplifier should be no problem. Remove the control panel, check the fan control switch and find that there is a small variable resistor inside, it is estimated that this is the manual air flow controller, a measurement of resistance, resistance changes, to confirm the bad here.
    After changing the fan control switch, measure the manual control of the air flow when the blower motor current, current from 4A to 17A grading changes, very good. Repair work is over.