Temperature Controls

CIRCUIT OPERATION
Two temperature variable resistors are connected to the Heater and A/C Control Assembly to provide in car and outside temperature information. These devices are thermistors which decrease in resistance as the temperature of the device increases. They are connected to fixed resistors in the Heater and A/C Control Assembly to provide a voltage input which varies according to the change in resistance.

Circuits within the Heater and A/C Control Assembly use the input from the In Car Sensor and the set temperature selected by the driver to determine whether the air should be heated or cooled to bring the inside of the car to the selected temperature. The input from the Outside Sensor is used to determine the amount of heating or cooling required to bring the temperature inside the car to the selected value as quickly as possible.

The Air Mix Valve Motor controls the position of the Air Mix Valve. The Motor can be operated in either direction by the polarity of the voltage applied to it. When the solid state switch grounds Terminal N in the Heater and A/C Control Assembly, then Terminal C of the Air Mix Valve Actuator is positive. If the condition of the solid state switches is reversed and Terminal M is grounded, then Terminal D of the Air Mix Valve Actuator is positive and the Motor runs in the reverse direction.

The Position Feedback Pot indicates the position of the Valve at any point of its travel. As the Valve moves between fully open and fully closed, the voltage input at Terminal C12 on the Heater and A/C Control Assembly will vary between zero and 5 volts.