For 1990-2009 cars

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

The heater-A/C control supplies battery voltage to the blower motor by way of the blower motor resistor. At low and medium speeds, the blower motor resistors step down the voltage. At high speed, the blower motor relay is energized, removing the blower motor resistors from the circuit. The relay then applies battery voltage directly to the blower motor through the relay. The motor then runs at maximum speed.

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

The auxiliary blower switch supplies battery voltage to the auxiliary blower motor switch by way of the auxiliary blower motor resistor. The auxiliary blower motor resistors step down the voltage at low and medium speeds. At high speed, the blower motor receives full voltage. Full voltage causes the blower motor to run at maximum speed.

The auxiliary heater-A/C control (auxilliary blower switch) controls the auxiliary blower motor when the rear window wiper/washer and multi-function switch (auxiliary blower switch) is in the rear position.