With Electronic 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 HVAC Control Head from temperature signal inputs and the operating mode of the Air Conditioning System. The HVAC Control Head accepts input requests from the driver by the front panel push 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 the two Data Lines to the HVAC Programmer to be processed. When processed the HVAC Programmer delivers a variable voltage to the Blower Power Module.

The blower speed output from the HVAC Programmer is at terminal "C2" and 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.

The output speed signal from terminal "C2" is an input to the Blower Control Module at terminal "B" of connector C2. An amplifier and driver circuit in the Blower Control Module supplies voltage between 4 and 12 volts to the Blower Motor according to the input signal at terminal "B".

The voltage at the Blower Motor is fed back to the HVAC Programmer at terminal "C3". This signal is used for better blower speed stability as well as indicating a failure in the Blower Motor circuitry.