General Information - Air Delivery & Temperature Controls - HVAC System - Automatic

The air doors that control the flow of air through the A/C module are operated by vacuum actuators. Solenoid valves located in the vacuum/electric solenoid apply vacuum to the actuators or vent the actuators. The solenoids are controlled by solid state circuits in the heater-A/C control. Push buttons in the heater-A/C control determine the A/C operating mode. Depending on the mode selected, the heater-A/C control determines which air doors should be operated.

Two air temperature sensors are used by the heater-A/C control. Their resistance decreases as temperature increases. The inside air temperature sensor measures the inside air temperature, and the ambient outside air temperature sensor measures the outside air temperature. The difference between the two sensor measurements is used by the control circuits to determine whether the incoming air should be cooled or warmed, and to what degree, in order to bring the inside air temperature to the selected temperature as quickly as possible. If a malfunction should occur in either the inside air or ambient outside air temperature sensor circuits, the heater-A/C control will set a trouble code. It will also substitute a temperature value of 75°F (24°C) if the inside air temperature sensor circuit is at fault or 49°F (9°C) if the ambient outside air temperature sensor circuit is at fault. The substitute temperature value(s) allow the system to continue operations.

The sun load temperature sensor determines the amount of sunlight produced by the sun. As the sunlight increases the sensors current increases. This sensor is used to program the blower speed and the auto/bi-level modes.