A/C Signal: Description and Operation

PURPOSE
This signal tells the Electronic Control Module (ECM) that the A/C selector switch is turned "ON" and that the A/C pressure switches are closed. The ECM uses this to adjust the idle speed before turning "ON" the A/C clutch, to disable the clutch during wide open throttle or during high power steering loads.

Note: If this signal is not available to the ECM, the A/C compressor will be inoperative.

OPERATION
The A/C clutch control relay is ECM controlled to delay A/C clutch engagement about 0.4 second after A/C is turned "ON". This allows the Idle Air Control (IAC) Valve to adjust engine RPM before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during wide open throttle, when high power steering pressure is present, or if engine is overheating. The A/C clutch control relay is energized when the ECM provides a ground path for circuit 459. The low pressure switch will open if A/C pressure is less than 276 kPa (40 psi). The high pressure switch will open if A/C pressure exceeds about 3034 kPa (440 psi). The A/C pressure fan switch opens when A/C pressure exceeds about 1380 kPa (200 psi).