System Components - Control

Controller
The operation of the A/C system is controlled by the switches and the lever on the control head. The compressor clutch and the blower are connected electrically to the control head by a wiring harness. The blower circuit is open in the OFF mode. Airflow is provided by the tour blower speeds available in the remaining modes. Cooled and dehumidified air is available in the MAX, NORMAL, BI-LEVEL, and DEFROST modes.

The temperature is controlled by the position of the temperature knob on the control head. A cable connects this knob to the temperature door, which controls the airflow through the heater core. As the temperature knob is moved through its range of travel, a sliding clip on the cable at the temperature valve connection should assume a position ensuring that the temperature door will seat in both extreme positions. The temperature door position is independent of the mode control switch. The temperature door on some models is controlled electrically, eliminating the need for the temperature cable.

The electric engine cooling fan on some vehicles is not part of the A/C control system; however, the fan is operational any time the A/C control is in the MAX, NORMAL, or BI-LEVEL modes. Some models provide for engine cooling fan operation when the controller is in the DEFROST mode. 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. On some models, the engine cooling fan will be turned off during road speed conditions above 56 km/h (35 mph), when the airflow though the condenser coil is adequate for efficient cooling. The operation of the cooling fan is controlled by the powertrain control module (PCM), or the engine control module (ECM), through the cooling fan relay.

Pressure Transducer
The pressure transducer 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 near the right front strut tower and the air filter assembly.

Wide-Open Throttle (WOT) Compressor Cutoff
During full throttle acceleration on vehicles equipped with multi-port injection (MPI), the throttle position sensor (PS) sends a signal to the PCM or the ECM, which then controls the compressor clutch.

A/C Time Delay Relay
This relay on some vehicles controls the current to the entire A/C system and provides a short delay of A/C operation upon start-up.