Blower Motor Resistor FAQ

Driving down the road, your car's HVAC fan suddenly stops and only works on the HIGH setting. Pictured above is a typical blower fan resistor module. They're mounted on a ceramic plate and uses a thermister which opens up if there is too much current going through it, generating heat.

During normal operation this device sits inside the air fan box of your blower fan module. It is kept cool by the air passing through it. Usually there are 3 or 4 speeds. They are not cheap, the one I replaced in my Mazda 3 cost $138! If I wanted a mechanic to install this device, it would have cost another $90 (or 238).

In the mazda it's really easy to replace:

1. Remove the bottom kickplate in the front passenger area. It simply pops off, along with the plate under the glove box.

2. Remove the 3 screws that house the fan blower module resistor. You'll need a flat head screw driver to pry the old blower motor resistor out of the plastic clip

3. Remove the old cabin air filters if you want and replace with new ones. (Do this every year)

4. Replace the resistor module. Important: Do NOT turn on the fan until the unit has been re-mounted into the air box. If you don't do this, you'll risk blowing the resistor module from over-heating.

Good luck.