The blower motor is the central component of the air conditioning system in BMW 3 Series, responsible for blowing hot or cold air through the AC vents. If the blower motor stops working due to a fault, the air will not flow out of the vents when you switch on the AC in your 3 Series.
The most common causes for AC fan blower motor not working in BMW 3 Series are blown fuse, bad relay, resistor or control module malfunction and faulty blower motor. However, a bad electrical connector or broken wire, or a defect in the climate control unit can also cause the blower motor to stop working.
1. Blown fuse
The AC blower motor in BMW 3 Series needs electricity to work. In case of a faulty fuse, the circuit is interrupted and the motor can not work.
Check the owners manual of your 3 Series or the fuse box cover to find the exact location of the fuse for the blower motor. If the fuse is blown, replace it with a new one with the specified amp rating.
To check the fuse, pull it out of the fuse box using a fuse puller or needle nose plier and hold it against the light. If the metal strip is broken in the middle, the fuse has blown. You must replace it with one of the same amperage and therefore the same color. It does not matter in which direction you insert the fuse.
2. Bad relay
Relays are electromagnetic switches that are used to switch electrical loads on and off. A bad relay can also be the cause of AC blower motor failure in your BMW 3 Series.
First of all, you should find out where the blower motor relay is located in your particular model of 3 Series. The information may be listed in your vehicle’s owners manual. Typically relays are located in the engine compartment or under the steering wheel on the left-hand side. If you are lucky, the wiring diagram will be drawn on the facing. You can test the relay by swapping it with other relays in the fuse box with similar amp rating. But before you begin the replacement, it is highly recommended to disconnect the vehicle’s battery.
3. Bad resistor or control module
The function of the blower motor resistor is to control the speed of the blower motor. When you increase or decrease the AC fan speed in your 3 Series, the climate control unit signals the resistor module to increase or decrease the flow of electric current to the blower motor. If the resistor module develops a fault, it can cause the blower motor to stop working.