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Different aspects of blower motor resistors and how it works?


The term blower motor refers to an electrically powered fan in a vehicle that provides air to the passenger compartment. The heater blower resistor regulates the rate at which the blower motor delivers this air. A blower motor resistor, usually found beneath the passenger side dashboard, comprises three resistors or sets of terminals designed to generate a voltage in proportion to electrical current. These resistors enable the blower motor to operate at slower speeds.


Blower motor resistors include controls for adjusting air settings. If the airflow exceeds a certain threshold, the blower motor resistor reduces airflow through the vents using wire coils. Each coil is in charge of a one-speed setting: Thinner coils correspond to higher air settings and provide the least resistance (opposing the flow of electric current), allowing the blower fan to rotate more quickly, whereas thicker coils correspond to lower air settings and force the fan to turn more slowly.


If the blower motor resistor fails, the blower motor will only operate at its maximum speed and will not be able to decelerate. This problem is usually resolved by replacing the blower motor resistor. The blower motor’s resistor is in charge of transferring the electrical current required to move air through the vehicle’s vents. 

Blower motor resistors can wear out, causing the blower motor to stop working properly. Several symptoms appear when the blower motor’s resistor fails. Recognizing these symptoms and replacing the resistor restores proper airflow through the car.

Operation is sporadic

When the blower motor’s resistor begins to fail, the motor only operates intermittently. This is frequently manifested by the blower fan not turning on until the engine produces a certain electric current. 

The higher wind can cause a jump across the bad resistor contacts, causing the blower motor to engage. On longer road trips, the blower motor may stop working again when the car is at cruising speed and the electrical current of the motor drops. Lower blower motor settings require less electrical current to engage. 

However, when the blower motor’s resistor fails, it causes a larger gap between the connectors. This chasm may be too wide for an electric current to pass through. When this happens, the lower settings of the blower motor are rendered inoperable. The blower motor’s top location may still be operational.

A blower motor stuck on one setting is a common symptom of a faulty blower motor resistor. The blower motor resistor is the component directly responsible for controlling the blower motor’s fan speed. If the resistor shorts or fails, the blower motor may become stuck at one fan speed. The heating and air conditioning systems may continue to operate at one speed, but the resistor must be replaced before full functionality can be restored.

Air Movement has been reduced

Reduced airflow occurs when the blower motor attempts to move air through the vents, but the resistor does not send enough power to move the stand with enough pressure. The blower motor resistor is getting power, but not all of it. 

Reduced air movement can occur at any of the motor blower’s speed settings. Depending on how much of the resistor remains functional, the reduced airflow could be an intermittent issue. A blower motor that does not function in certain settings is another common symptom of a faulty blower motor resistor. 

If the internal components of the blower motor resistors fail, the blower motor may malfunction or not function at all on one or more of the settings. A faulty blower motor switch can also cause this, so a proper diagnosis is highly recommended if you are unsure of the problem.

How do you put a blower motor through its paces?

If the blower motor does not function properly, the blower motor must first be tested. When the blower motor is turned on, the voltage at the blower motor connector is typically measured. If there is a voltage at the motor (at least 4-6 Volts at low speed and 12 Volts at high speed), but the motor does not run. The engine is defective or jammed. Leaves, twigs, nuts, and pieces of a ripped cabin filter can all jam the blower motor’s blade. 

This is a common occurrence in many automobiles. If no voltage is present at the motor, the entire blower motor circuit must be tested, beginning with a fuse. If a blower motor fails, it must be replaced. Depending on the vehicle, replacing the blower motor ranges from $320 to $650. The blower motor is located behind the glove box in many cars and is held in place by 3-4 screws. In others, it may be located inside the dash (as in the Mazda 5), making replacement difficult.

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