The Hvac Blower motor resistor.

a/c air flow controls

 

The function of a blower motor resistor.

The function of a blower resistor is to slow down the blower various speeds by way of a voltage drop.

In the high position, the resistor is bypassed by a relay on many systems and full voltage is supplied to the motor. There are multiple resistance taps on the resistor block that make up each speed. 

Resistance, voltage drop and blower speed.

The more resistance, the greater the voltage drop and the lower the blower speed .