Heating and Air Conditioning: Description and Operation

The automatic A/C system automatically controls operation of the A/C compressor, air inlet door, water valve and blower fan in order to maintain passenger compartment temperature within the range selected by the operator.
The system control circuit consists of a feedback potentiometer, temperature control rheostat and ambient and in-car temperature sensors which are connected in series to provide a variable resistance to system input voltage. The output voltage of this control circuit is applied to an amplifier which transforms the control signal into an operating voltage that is proportional to the control circuit voltage signal. The amplifier output voltage is converted to a modulated vacuum signal in the vacuum valve, the vacuum signal is applied to the power servo, and the power servo controls system operation.