What it does
The blower motor resistor controls the speed of the fan that blows heat and A/C into the cabin. On most traditional systems, the lower speeds run through the resistor while high bypasses it. Some newer vehicles use an electronic blower control module instead.
Common symptoms
- The fan only works on high
- Some fan speeds work and others don't
- A melted or burnt-looking connector at the resistor
If the fan doesn't work on any speed, it's usually something else, like a blown fuse, a bad blower motor, the switch or wiring.
What to look for
- Test every speed: run the fan through each setting and note which ones work.
- Find the resistor: it's usually mounted near the blower motor, often under the passenger side of the dash.
- Check the connector: melted, browned or burnt plastic is a common sign.
Could be something else
A worn blower motor can pull too much current and burn out the resistor. If you only replace the resistor, the new one can fail too, so the motor should be checked.
Is it safe to drive?
The vehicle drives fine, but you need your defroster to see in winter. If high still works, you have defrost for now. Get it fixed before it quits completely.
Related: Bad thermostat symptoms · Winter car survival kit
Heater fan acting up? Northwoods tracks down electrical problems right where your vehicle sits.