Blower Motor Resistor
An electrical component that regulates the speed of the HVAC blower motor by adjusting resistance in the circuit.
The blower motor resistor is an electrical switch component that controls the speed of the cabin heating and air conditioning (HVAC) fan. When you change the fan speed setting on the dashboard, the resistor pack adjusts the electrical resistance to limit current to the fan.
By increasing or decreasing resistance, the resistor reduces the voltage sent to the blower motor, slowing it down. On the highest fan speed setting, the switch usually bypasses the resistor entirely, sending full 12-volt battery power to the motor.
Because it converts excess electrical energy into heat, the resistor pack is mounted inside the HVAC ducting so that the flowing cabin air cools it. If the airflow is restricted (such as by a clogged cabin air filter) or the blower motor draws too much current, the resistor will overheat and burn out.
The classic sign of a failed blower motor resistor is a fan that only works on the highest speed setting, or a fan that refuses to turn on at all. Replacing the resistor is a common HVAC fix.