If your BMW's heater or air conditioner fan won't turn on or only works on the "high" setting, the blower resistor is likely worn out. You can save some money and replace the resistor yourself using some basic hand tools. A replacement resistor can be obtained from your local BMW dealership, or you can purchase one through an auto parts store.
Unscrew the two screws holding the dash panel underneath the steering wheel in place. There is one screw in each of the top corners. Use a Phillips screwdriver to remove them. Pull the panel off.
Remove the metal shield that is now exposed. Use a 10mm socket to unbolt the three bolts that secure it, then pull the shield out.
Remove the OBD-II diagnostic port with a Phillips screwdriver and push it aside. It is not necessary to disconnect the wiring from the port. Remove the plastic air duct by gently pulling on it until the plastic clips release. The blower resistor is now exposed. It is the small, rectangular box that was previously hidden by the duct.
Unbolt the resistor with a Torx-20 screwdriver. Pull it out and insert the replacement resistor. Tighten the screws firmly. Test the system to make sure the blower motor now works properly, then reassemble the parts that were previously removed, ensuring all screws and bolts are replaced.