Air Conditioning (A/C) Controls

AIR CONDITIONING (A/C) CONTROLS-PCM INPUT

The A/C control system information applies to factory installed air conditioning units.

A/C SELECT SIGNAL:
When the A/C switch is in the ON position, an input signal is sent to the Powertrain Control Module (PCM). The signal informs the PCM that the A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the Idle Air Control (IAC) motor to compensate for increased engine load.

A/C REQUEST SIGNAL:
Once A/C has been selected, the PCM receives the A/C request signal from the clutch cycling pressure switch. The input indicates that the evaporator pressure is in the proper range for A/C application. The PCM uses this input to cycle the A/C compressor clutch (through the A/C relay). It will also determine the correct engine idle speed through the IAC motor position.

If the A/C low-pressure switch or high-pressure switch opens (indicating a low or high refrigerant pressure), the PCM will not receive an A/C request signal. The PCM will then remove the ground from the A/C relay. This will deactivate the A/C compressor clutch.

If the switch opens, (indicating that evaporator is not in proper pressure range), the PCM will not receive the A/C request signal. The PCM will then remove the ground from the A/C relay deactivating the A/C compressor clutch.