What Does a Blower Motor Resistor Do?

by Andrea Stein
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"Blower motor" refers to an electrically operated fan in a vehicle that supplies air to the passenger compartment. The heater blower resistor helps control the rate at which the blower motor supplies this air.


A blower motor resistor, typically located beneath the passenger side dashboard, contains three resistors, or sets of terminals designed to generate voltage in proportion to electrical current. These resistors allow the blower motor to function at lower speeds.


Blower motor resistors contain controls that determine air settings. If the airflow exceeds a predetermined amount, the blower motor resistor reduces airflow through the vents via wire coils. Each coil is responsible for one speed setting: Thinner coils correspond to higher air settings and offer the least resistance (the least opposition to the flow of electric current), allowing the blower fan to rotate faster, while thicker coils correspond to lower air settings and force the fan to rotate more slowly.


If the blower motor resistor fails, the blower motor only functions at its highest speed and cannot decelerate. Replacing the blower motor resistor typically corrects this problem.

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