The heater resistor controls the rate at which the heater blower motor supplies the air. When the heater resistor fails, the blower motor only functions are certain speeds.
Before you rush out to replace your heater resistor, check to make sure that it is not the heater motor, wiring, fuses or heater switch that is the issue. If you are still experiencing problems with your heater fan controls, it is most likely the heater resistor will need replacing.
The Heater Resistor can be easily replaced at low cost with basic mechanical knowledge.