A heater resistor is used to control the speed of the blower fan motor. In some vehicles the resistor is also used to control the air conditioning in a vehicle. Some SUVs or vans have a separate heater resistor in the front of the vehicle and one in the rear as they have two heater systems in the vehicle.

If a heater resistor fails, you may find that the heater fan will no longer blow on one or all of the in-vehicle settings. If the blower motor is causing problems, you could notice that using the vehicle’s heating or air conditioning system is noisy, which could be caused by a failing heater resistor. On inspection of a failed heater resistor, you will most likely find points on the resistor that are burnt. This could be caused by an unnatural amount of load on the heater resistor fan. This could be caused by insulation from around the fan being dragged in to the fan, causing it to struggle to turn freely. resistor failure can also be caused by the bearings of the fan becoming damaged, resulting in excessive draw.