The resistor of the blower motor is responsible for transferring the electrical current that's required to move air through the vents of vehicle. Blower motor resistors can wear out; the blower motor no longer works correctly if this occurs. There are several symptoms that appear when the resistor of the blower motor is going bad. Recognising these symptoms and replacing the resistor returns the airflow through the car to the proper levels.
When the resister of the blower motor starts to fail, the motor operates only intermittently. This often presents itself as the blower fan not kicking on until the engine is producing a certain level of electric current. The higher current can make the jump across the resistor contacts that are going bad and get the blower motor to engage. The blower motor could stop working again on longer roadtrips when the car is at a cruising speed and the electrical current of the motor drops again.
No Lower Settings
The lower settings of the blower motor require less electrical current to engage. But when the resistor of the blower motor is failing, it creates a larger gap between the connectors. This gap may be too far for the electric current to travel across. When this happens, the lower settings of the blower motor aren't able to function. The top setting of the blower motor may still be operational.
Reduced Air Movement
Reduced airflow is when the blower motor is trying to move air through the vents but the resistor isn't sending enough power to move the air with much pressure. The blower motor resistor is receiving power but not the full force. Reduced air movement can occur at all of the different speed settings of the motor blower. Depending on how much resistor is still functioning, the reduced airflow could be an intermittent problem.