The blower motor resistor is an electrical component that is a part of the vehicle's heating and air conditioning system. It is responsible for controlling the blower motor’s fan speed. When fan speed is changed via the knob on the instrument cluster, the blower motor resistor changes setting, which changes the speed of the blower motor. As the fan speed is one of the most frequently adjusted settings of the air conditioning system, the blower motor resistor is put under constant stress, which can cause it to eventually fail. A failed blower motor resistor can cause issues with the operation of the entire heating and air conditioning system. Usually a bad or failing blower motor resistor will produce a few symptoms that can alert the driver of a potential issue.
1. Blower motor stuck on one speed
A common symptom of a faulty blower motor resistor is a blower motor that is stuck on one setting. The blower motor resistor is the component directly responsible for controlling the blower motor fan speed. If the resistor shorts or fails, it may cause the blower motor to remain stuck on one fan speed. The heating and air conditioning systems may still function at one speed, however the resistor will have to be replaced in order for full functionality to be restored.
2. Blower motor does not work on certain settings
Another common symptom of a faulty blower motor resistor is a a blower motor that does not function on certain settings. If the blower motor resistors’ internal components fail it may cause the blower motor to malfunction, or not function at all on one or more of the settings. This can also be caused by a blower motor switch, so a proper diagnosis is highly recommended if you are uncertain of what the issue may be.
3. No air from the vehicle’s vents
Another symptom of a faulty blower motor resistor is no air from the vehicle’s vents at all. Power to the blower motor is fed through the blower motor resistor, so if it fails or has any issues power can be cut off to the motor. A blower motor without power will not be able to produce any air pressure, and as a result the heating and air conditioning system will be left with no air coming from the vents.
As the blower motor resistor is the component directly responsible for powering the blower motor, when it fails it major issues with the blower motor and the heating and air conditioning system can be experienced. If your vehicle is displaying any of the symptoms above, or you suspect that your blower motor resistor may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the component should be replaced.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Heater Blower Motor Resistor and was authored by Eduardo Ruelas.