A/c Compressor Clutch Controls Chevrolet Cab & Chassis C3500

MODEL IDENTIFICATION

Note. The following figures are courtesy of General Motors Corp.

SERIES CODE DESIGNATIONS (LIGHT TRUCKS & VANS)

DESCRIPTION & OPERATION

Note. The "C" and "K" Series trucks use an Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM) to maintain engine idle speed during A/C compressor clutch operation.

On vehicles with a Powertrain Control Module (PCM) controlled A/C compressor clutch, the A/C compressor clutch relay is controlled by the PCM. The PCM improves idle quality by delaying A/C compressor clutch engagement until idle speed is increased, and disengages A/C compressor clutch when idle speed is too low. A/C compressor clutch is cycled by PCM. PCM smooths cycling of A/C compressor clutch by adding fuel the instant A/C compressor clutch is applied.

On vehicles without a PCM-controlled A/C compressor clutch, turning on A/C system supplies battery voltage to the A/C compressor clutch and A/C request signal terminal of Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM). When the ECM, PCM or VCM sees battery voltage at A/C request signal terminal, it maintains idle speed. The ECM, PCM or VCM does not control A/C compressor clutch operation. An A/C pressure cycling switch is used to control A/C compressor clutch operation.

TROUBLE SHOOTING

Note. This article contains test flow charts which are part of General Motors Computerized Engine Controls. Only those flow charts required to test A/C compressor clutch control are included. Other diagnostic information may be referenced while performing A/C compressor clutch control diagnosis. For complete information on General Motors Computerized Engine Control systems, see appropriate articles in ENGINE PERFORMANCE section.

TROUBLE SHOOTING CHART DIRECTORY

A/C COMPRESSOR CLUTCH CHART INDEX

SCAN TESTER

A variety of information is transmitted through Data Link Connector (DLC) terminal "E" or "M", depending on engine. This data is transmitted at a high frequency which requires a Tech 1 scan tester for interpretation. Several scan testers are available for diagnostic work. Scan testers other than Tech 1 scan tester will function and provide information for diagnostic work; however, some flow charts will specify a Tech 1 scan tester. Failure to use a Tech 1 scan tester when specified may result in incorrect diagnosis of a system.

A/C Request Signal Ckt. Diagnostic Schematic 4.3L, 5.0L, 5.7L, 7.4L. Scheme 1

A/C REQUEST SIGNAL CIRCUIT DIAGNOSIS (M/T)

Turning on A/C system supplies battery voltage to A/C compressor clutch and Engine Control Module (ECM) terminal B8 through circuit No. 59, increasing idle speed. ECM 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 circuit No. 59 to ECM. If circuit No. 59 is okay, repair faulty ECM connection or replace faulty ECM.

A/C Request Signal Circuit Diagnostic Schematic (M/T). Scheme 2

A/C REQUEST SIGNAL CIRCUIT DIAGNOSIS (6.5L)

Turning on A/C system supplies battery voltage to A/C compressor clutch and Powertrain Control Module (PCM) terminal B4 through circuit No. 59, 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 circuit No. 59 to PCM. If circuit No. 59 is okay, repair faulty PCM connection or replace faulty PCM.

A/C Request Signal Circuit Diagnostic Schematic (6.5L). Scheme 3