The blower motor is a variable speed motor. The motor operates at a higher rate when voltage is increased to the maximum level.

The blower motor resistors step down the voltage supplied from Fuse 4 when the blower control is set at low and medium speeds. The blower motor relay energizes at high speed, removing the blower motor resistor from the circuit. The battery voltage is then applied directly from Fuse 14 to the blower motor though the relay, causing the motor to run at high speed.