Blower Controls

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 Electronic A/C Control Head from temperature signal inputs and the operating mode of the Air Conditioning System in the "AUTO" mode or, by the driver manually, from the Blower Control Fan "UP" or Fan "DOWN" buttons.

When the blower speed is determined either automatically in the AUTO Fan mode, or manually by the driver, the Control Head sends this information along to the Electronic A/C Power Module to amplify the signal. When amplified, the Electronic A/C Power Module delivers a variable voltage to the Power Module.

The blower speed output to the Electronic A/C Power Module is a continuously variable voltage, proportional to blower speed. At minimum blower speed the output is about 2.5 volts and at maximum blower speed it is about 7 volts.

An amplifier and driver circuit in the Power Module supplies voltage between 4 and 12 volts to the Blower Motor according to the input signal from the Control Head.

The voltage at the Blower Motor is fed back to the Control Head. This signal is used for better blower speed stability as well as indicating a failure in the Blower Motor circuitry.