Circuit Operation

CIRCUIT OPERATION
(TEMPERATURE CONTROL)
Three temperature variable resistors (sensors) are connected to the Electronic 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. The one exception to this is the Solar Sensor, which is a Photo Diode. The Photo Diode output decreases with increasing light intensity. These sensors are connected to fixed resistors in the Control Assembly to provide a voltage input which varies according to the change in resistance. Ground reference for the sensors is provided by the Control Assembly. Circuits within the Control Assembly use the input from the In-Car Sensor and the Sun Load 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 vehicle to the selected temperature. The input from the Ambient 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 Air Mix Door Motor controls the position of the Temperature 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 "F" in the Electronic A/C Control Assembly, then terminal "5" of the Air Mix Door Motor is positive. If the condition of the solid state switches is reversed and terminal "G" is grounded, then terminal "6" of the Air Mix Door Motor is positive and the motor runs in the reverse direction. The Position Feedback Pot indicates the position of the Temperature Valve at any point of its travel. As the Temperature Valve moves between fully open and fully closed, the voltage input at terminal "6" on the Electronic A/C Control Assembly will vary between .5 and 5 volts. When a problem is detected with the temperature control system, certain malfunction codes may be set. A further description of these codes as well as diagnosis, will be found in SECTION 1C1-12 (1991 and 1992 Early Production) or SECTION 1C-12 (1992 Late Production).