The blower motor is a variable speed motor. The higher the voltage applied to the motor, the faster the speed.

Battery voltage to the blower motor is supplied by the heater-A/C control through the blower motor resistor. At low and medium speeds, the voltage is stepped down by the internal blower motor resistors. Each internal resistor also has a thermal limiter in series with it. At high speed, the internal blower motor relay is energized, removing the blower motor resistors from the circuit. Battery voltage is then applied directly to the blower motor through the relay. The motor will then run at maximum speed.