System Components - Control

Controller
The operation of the A/C system is controlled by the switches on the control head. This console-mounted heating-and-ventilation panel contains the following:

Three rotary control knobs
1. The rotary temperature control knob:
- Actuates by cable.
- Varies the mix of the fresh air from outside the vehicle with the heated air from inside the vehicle to suit individual preference.
- Raises the temperature of the air entering the vehicle by rotation toward the right, or the red portion of the knob.

2. The rotary mode control knob:
- Actuates by vacuum.
- Regulates the air distribution between the windshield, the instrument panel, and the floor vents.

3. The rotary blower control knob:
- Turns ON to operate the blower motor at four speeds.
- Turns OFF to stop the blower.
- Operates completely independently from both the mode control knob, that regulates the defroster door, and the temperature control knob.
- Changes the fan speed in any mode and at any temperature setting. However, if the rotary blower control knob is OFF, the A/C system is OFF, regardless of the position of the A/C push knob.

Three push knobs
1. The A/C push knob:
- Controls the A/C.
- Turns the A/C ON when the push knob is pressed and the indicator lamp is illuminated. (The rotary blower control knob must be in one of its four positions for the A/C to function.)

2. The rear window defogger push knob:
- Controls the rear window defogger.
- Turns ON the rear window defogger when the push knob is pressed and the indicator lamp is illuminated.

3. The fresh air control push knob:
- Switches between recirculating passenger compartment air or bringing outside air into the passenger compartment.
- Defaults to fresh air mode. The indicator lamp is illuminated when recirculation is selected.
- Operates the inlet air door by vacuum.

The engine cooling fans are operational any time the A/C control is on. This added feature is part of the A/C controller function and is aimed at preventing excessive compressor head temperatures. It also allows the A/C system to function more efficiently. The operation of the cooling fans is controlled by the engine control module (ECM) through the cooling fan relays.

Vacuum Lines
Vacuum lines are molded to a connector, which is attached to a vacuum control switch on the control head assembly.

In case of leakage or hose collapse, it will not be necessary to replace the entire harness assembly. Replacement can be made by cutting the hose and inserting a plastic connector. If an entire hose must be replaced, cut all the hoses off at the connector and attach hoses directly to the control head vacuum switch.

Vacuum Tank
During heavy acceleration, the vacuum supply from the manifold drops. A check valve in the vacuum tank maintains vacuum so that under load conditions vacuum will be available for continuous use.

Pressure Transducer
Pressure transducer switching incorporates the functions of the high-pressure and the low-pressure cutout switches along with the fan cycling switch. The pressure transducer is located in the high-side liquid refrigerant line behind the right headlamp, between the right front inner fender and the air filter assembly. The output from this pressure transducer goes to the ECM which controls the compressor function based on the pressure signal.

Wide-Open Throttle (WOT) Compressor Cutoff
During full throttle acceleration, the throttle position sensor (TPS) sends a signal to the ECM, which then controls the compressor clutch.