The heater resistor is also known as the heater blower motor resistor or blower speed controller because it fundamentally controls the fan speed of the interior heater. In this TechASSIST guide we look at the types of resistors, causes and symptoms of failure and offer advice on diagnosing faults.
Original type heater resistors
The original resistor based blower motor control was a simple resistor winding arrangement. Vehicles fitted with this type of resistor would typically have 4 fan speed settings for the driver to choose from. As the resistance is changed and the voltage through the motor is increased or decreased to control the speed of the blower motor/fan.