A/C Signal: Description and Operation

PURPOSE
Powertrain Control Module (PCM) monitors engine load and A/C system pressure, and cycles the A/C compressor clutch accordingly.

OPERATION
When the A/C switch turned ON, and the A/C low pressure switch is closed, the PCM receives an A/C SELECTED signal.

- The PCM increases engine speed, via the Idle Air Control (IAC) motor, to compensate for increased engine load, (due to A/C compressor).

- PCM looks for an A/C REQUESTED input, (closed evaporator switch, indicating the evaporator is within the proper temperature range).

When the PCM receives an A/C REQUESTED input, (evaporator switch closed), the PCM engages the A/C compressor clutch (by grounding the clutch relay).

- The PCM cycles the compressor clutch, depending on engine load and A/C system pressure. If the PCM receives a signal from the A/C low pressure switch (indicating low Freon level), or evaporator electric clutch cycling switch, (indicating evaporator freezing), the PCM will de-energize the clutch relay.

- The PCM maintains correct engine idle speed, through the Idle Air Control (IAC) Motor.