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/hi-level modes.

Air Inlet Valve
The air inlet valve is closed in most of the operating modes permitting outside air to enter the A/C module. It is opened only in the A/C modes and at a temperature setting of 65°F (18°C) or higher. When open, air from inside the vehicle is recirculated to get maximum cooling.

Air Temperature Valves
The air temperature valves are positioned by the left and right electric actuators. When the door is in the COOL position, air is prevented from passing through the beater core. The door can be placed by the actuator in any position between COOL and WARM to provide any degree of warming to the air after it has passed through the A/C evaporator core.

Defroster Valve and Heater Outlet Valve
The defroster valve and the heater outlet valve are connected together by a mechanical linkage allowing the two valves to move together. The defroster valve and heater outlet valve can be moved to one of three positions. The heater/defroster mode valve vacuum actuator consists of two chambers operated by two vacuum actuators. When the A/C system is operated in the defog mode, both vacuum chambers are vented and both doors are in position B. Airflow is then directed to both the defroster outlets and heater outlets. If the #2 solenoid is activated, the actuator will move the valves to position A, which directs airflow to the heater outlets lower mode. If the #1 solenoid is activated, the valves move to direct air to the defrost outlets. Position C is the position the valves are in when operating in the defrost mode.

Vent Valve
The vent valve is in position A when the #5 solenoid (A/C) is activated (lower. defog or defrost modes). In this position, airflow is directed out of the A/C outlets. The vent valve is in position C when the #3 solenoid (bi-level) is activated (upper mode). In this position, airflow is directed out of the I/P vents. When neither solenoid is activated (hi-level mode) the vent valve is in the B or neutral position. This directs air out of both the I/P outlet and the floor outlets.

Delay Mode
The delay mode is used to prevent the vehicle occupants' breath from fogging the windshield when the outside temperature is low and the engine is cold. The heater-A/C control will set the doors so that airflow is directed to the windshield with low blower operation. The system will stay in the delay mode until engine coolant temperature reaches 49°C (120°F) or after 4 minutes, whichever comes first. The system will then operate normally in the selected mode.