MODEL IDENTIFICATION
| Model | (1) Series Designation |
|---|---|
| 2WD Models | "C" |
| 4WD Models | "K" |
| (1) Series codes determined by fifth character of VIN code | |
| (1) | Series codes determined by fifth character of VIN code |
BODY CODE DESIGNATIONS
DESCRIPTION & OPERATION
Note. All "C" & "K" trucks use Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM) to maintain engine idle speed during A/C compressor clutch operation. These trucks do not use ECM, PCM or VCM to control A/C compressor clutch circuit.
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 charts which are part of General Motors Computerized Engine Controls. Only those 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 the G-TESTS W/CODES article in the ENGINE PERFORMANCE section.
Trouble shoot A/C compressor clutch control using appropriate schematic and diagnostic charts. See TROUBLE SHOOTING CHART DIRECTORY.
TROUBLE SHOOTING CHART DIRECTORY
| Application | See Figure |
|---|---|
| 4.3L VIN Z | (Scheme 1) |
| 5.0L VIN H | (Scheme 1) |
| 5.7L VIN K | (Scheme 1) |
| 6.5L VIN F, P & S | (Scheme 2) |
| 7.4L VIN N | (Scheme 1) |
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 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 CIRCUIT DIAGNOSIS 4.3L - VIN W & Z, 5.0L - VIN H, 5.7L - VIN K, 7.4L - VIN N
Turning on A/C system supplies battery voltage to A/C compressor clutch and Powertrain Control Module (PCM) terminal E12 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 (terminal E12) or replace faulty PCM.
Scheme 1
A/C REQUEST SIGNAL CIRCUIT DIAGNOSIS 6.5L - VIN F, P & S
Turning on A/C system supplies battery voltage to A/C compressor clutch and Powertrain Control Module (PCM) terminal PB4 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 (terminal PB4) or replace faulty PCM.
