Compressor Controls

DESCRIPTION
In order to improve engine operation, and protect the A/C compressor and clutch during Wide Open Throttle (WOT) performance, the A/C compressor operation is controlled by the PCM.

OPERATION
The A/C electrical system consists of an A/C control head, A/C refrigerant low pressure cutoff switch, an A/C refrigerant pressure sensor, an evaporator temperature sensor, a control relay, the compressor clutch, and the PCM.

When A/C is selected "ON" through the A/C control head, a 12 volt signal is supplied to the A/C request input of the PCM. The PCM will poll the A/C refrigerant pressure sensor and A/C evaporator temperature sensor before enabling the compressor clutch control relay. If either switch detects a pressure or temperature variation above or below a calibrated acceptable range, the clutch relay will not be enabled. When the PCM determines that the system temperature and pressure are within acceptable ranges, the A/C compressor clutch relay will be enabled, allowing voltage to be applied to the A/C clutch and A/C status input of the PCM. The A/C status input informs the PCM that the relay has closed and voltage is applied to the clutch, via the A/C compressor low pressure cutoff switch. The A/C compressor low pressure cutoff switch is closed when there is sufficient system pressure (depending on refrigerant charge and ambient temperature). The PCM will also turn the cooling fan "ON" when A/C is requested. Refer to Cooling System for more information on cooling fan operation. A/C is controlled by the PCM so that the PCM can increase idle speed before turning "ON" the clutch or disable the clutch during WOT or high coolant temperatures.