Automatic

The speed of the Blower Motor is determined by the voltage applied to the motor. At low blower speeds the applied voltage is about 4 volts. As the voltage is increased, the blower speed increases until maximum blower speed is reached at 12 volts.
The speed at which the blower runs is determined by the Heater And A/C Control Assembly from temperature signal inputs and the operating mode of the Air Conditioning System. The Heater And A/C Control Assembly accepts input requests from the driver by the front panel push-button.
The blower speed output from the Heater And A/C Control Assembly is a continuously variable voltage, proportional to blower speed. At minimum blower speed the output is 0.5 volts and at maximum blower speed it is about 7 volts. Medium blower speed is 4 volts.
The blower speed output signal is an input to the Heater And A/C Power Module. An amplifier and driver circuit in the Heater And A/C Power Module supplies voltage between 4 and 12 volts to Blower Motor according to the blower speed input signal.
The voltage at the Blower Motor is fed back to the Heater And A/C Control Assembly at the blower feedback signal input terminal to allow precise speed control of the blower by the circuits in the Heater And A/C Control Assembly.