A/C Request Signal Circuit Diagnosis

Turning on A/C system supplies battery voltage to A/C compressor clutch and Powertrain Control Module (PCM). PCM responds by increasing idle speed. PCM does not control A/C compressor clutch. If A/C compressor clutch is malfunctioning, repair basic A/C system problem. If A/C system is operating properly and idle speed drops too low when A/C compressor turns on or flares too high when A/C compressor turns off, check for an open A/C signal circuit to PCM. See Fig 1. If circuit is okay, repair faulty PCM connection or replace faulty PCM.

Fig 1: A/C Clutch Circuit Diagram ("P" Series)

Courtesy of GENERAL MOTORS CORP.