The resistor can be found underneath the dashboard at the heater compartment of a blower motor. The resistor allows the blower motor to change the fan speed.
Without the resistor, the user cannot alter the speed of the airflow from the fan. Also, the heater blower may not work at all if the resistor fails. The air system of a vehicle is a closed system and is rarely inspected during the regular check up. Any time the heating system behaves unexpectedly, the vehicle should be taken in for inspection. Any mechanical resistance to the fan may cause damage to the heater blower system.