The air volume selection of the automatic air conditioner of this vehicle, whether automatic or manual, is divided into six grades from low to high. First, confirm the fault symptoms and switch the automatic and manual switches to the automatic position. According to the set temperature, the air volume of the air conditioner can change continuously from weak to strong, but when switching to manual position, even if the temperature is set very low, the air volume is unstable and occasionally very large. When the temperature setting is high, the air volume changes little.
This means that it is impossible to manually adjust from small air volume to large air volume.
Set the temperature to a high level in the manual position, or set the temperature to the lowest level in the automatic position, and you can clearly hear the action sound of the relay and the rotation sound of the blower. It should be said that there is nothing wrong with the power supply and motor.
The blower motor is equipped with a three-pin connector, which is about a power transistor. Two thick lines are power lines and one thin line is control line.
Change the set temperature in the automatic state and confirm the voltage of the control line. The voltage does change with the set temperature, but the air flow changes with the voltage, so the power transistor is normal.
In manual mode, when the fan switch is adjusted from LO (low temperature) position to HI (high temperature) position, the voltage change is unstable, so the air volume change is also unstable. Its principle is that when operating the fan switch, the base current of the power transistor is divided into six grades, so the collector and emitter voltages of the power transistor are also divided into six grades, so the voltage applied to the blower motor is also divided into six grades, so there are six grades of air volume.
When the air conditioner of this vehicle is in the state of automatic adjustment, the fan motor voltage can change continuously, so there should be no problem with the automatic air conditioner amplifier. Remove the control panel and check the fan control switch. It is found that there is a small variable resistor in it, which is a manual airflow controller. If the resistance changes, that's the problem here! I hope it helps you!