A/C Signal: Description and Operation

PURPOSE
This signal tells the Engine Control Module (ECM) that the Air Conditioning (A/C) Selector Switch is turned "ON". The ECM uses this to adjust the Idle speed, before turning "ON" the A/C Clutch. If this signal is not available to the ECM, the A/C Compressor will be inoperative. See Diagnostic Charts / Chart C-10 for A/C wiring diagrams and diagnosis of A/C electrical system. Chart C-10: Air Conditioning System Function Check