Temperature Control

One photosensitive and two temperature variable resistors (sensors) are connected to the Heater/vent/Air Conditioning (HVAC) Programmer to provide in-car and outside temperature information. The Inside Air Temperature and Outside Sensors are thermistors which decrease in resistance as the temperature of the device increases. The Sun Load Sensor resistance decreases as light increases. These sensors are connected to fixed resistors in the HVAC Programmer to provide a voltage input which varies according to the change in resistance. Ground reference for the sensors is provided by the HVAC Programmer.

Circuits within the HVAC Programmer use the input from the Inside Air Temperature Sensor and the Sun Load Sensor in conjunction with the set temperature selected to determine whether the air should be heated or cooled to bring the inside of the vehicle to the selected temperature. The input from the Outside Air Temperature Sensor is used to determine the amount of heating or cooling required to bring the temperature inside the vehicle to the selected value as quickly as possible.

The Temperature Door 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 "C8" in the HVAC Programmer, then terminal "5" of the Temperature Door Motor is positive. If the condition of the solid state switches is reversed and terminal "C7" is grounded, then terminal "6" of the Temperature Door Motor 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 "D13" on the HVAC Programmer will vary between 0 and 5 volts.