The heater blower motor resistor is an electronic device that allows the heater blower motor to operate at slower speeds. Since the highest speed of the blower motor is not controlled by the resistor, the fan will often work on the highest speed setting only when the blower motor resistor fails. When it fails, then a heater blower motor resistor replacement is needed.
The blower motor resistor is usually located under the dashboard, near the blower motor. To perform a heater blower motor resistor replacement, the technician disconnects the resistor's electrical connector and removes the old resistor. Then the new blower motor resistor is installed. Depending upon the vehicle, the resistor may be easily accessible or it may take partial dashboard removal to replace the resistor.
Some manufacturer factory warranties cover the cost of a heater blower motor resistor replacement under their bumper-to-bumper warranty. After the factory warranty expires, there may be an extended auto warranty available that will cover the cost of replacement of blower motor resistor, depending upon the level of coverage you choose.