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A/c Compressor Clutch Controls (G Series) Chevrolet Chevy Van G2500

A/c Compressor ~1205 words

DESCRIPTION & OPERATION

WARNINGTo avoid injury from accidental air bag deployment, read and follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article in the ACCESSORIES/SAFETY EQUIPMENT section.

Note. Powertrain Control Module (PCM) may also be known as Vehicle Control Module (VCM).

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, or 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.

TROUBLE SHOOTING

Note. This article contains testing that is part of General Motors Computerized Engine Controls. Only testing procedures required to test A/C compressor clutch control circuit is 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 TESTS W/CODES article in the ENGINE PERFORMANCE section.

RELAY LOCATION

ApplicationLocation
"G" SeriesIn Underhood Fuse/Relay Center, At Left Front Of Engine Compartment

A/C COMPRESSOR CLUTCH RELAY LOCATION

SCAN TOOL

A variety of information is transmitted through Data Link Connector (DLC). This data is transmitted at a high frequency which requires a Tech 1 scan tool, appropriate cartridge kit and vehicle interface module kit, or other scan tool for interpretation. Several scan tools are available for diagnostic work. Scan tools other than Tech 1 scan tool will function and provide information for diagnostic work.

WARNINGVehicles may be equipped with a PCM using an Electronically Erasable Programmable Read Only Memory (EEPROM). When replacing PCM, the new PCM must be programmed.

Note. To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary.

A/C CLUTCH CIRCUIT DIAGNOSIS

Note. 6.5L diesel engines are equipped with a Powertrain Control Module (PCM). Substitute PCM for VCM in the following test when diagnosing vehicles equipped with diesel engines.

Description

A/C clutch relay is controlled by Vehicle Control Module (VCM) to delay A/C clutch engagement after A/C is turned on. This allows VCM to adjust engine RPM before A/C clutch engages. VCM will engage A/C clutch any time A/C has been requested unless coolant temperature is high, A/C system pressure is low, A/C system pressure is high, wide open throttle, or high engine RPM.

When A/C-heater control panel is placed in A/C mode, a 12-volt signal is sent to VCM. When VCM receives this signal, VCM will ground A/C clutch relay control circuit to energize A/C relay. This is shown on scan tool as A/C REQUEST YES.

When an A/C request has been detected by VCM, VCM will ground A/C clutch relay control circuit. As a result, relay contacts close, allowing current to flow through relay to A/C compressor clutch. When A/C REQUEST has been detected by PCM, cooling fans will be turned on when A/C pressure is greater than a predetermined value.

Compressor Clutch Control Circuit Diagnosis

  1. Install A/C manifold gauge set. Ensure A/C system is fully charged. Charge system if necessary and go to next step.
  2. Start engine and allow it to reach normal operating temperature. Turn on A/C. If A/C compressor clutch engages, then disengages within 60 seconds, go to the «A/C-HEATER SYSTEM TROUBLE SHOOTING - MANUAL»(/chevrolet/chevy-van-g2500/1996-1998/remont/manual-hvac-system/#hvac-system-manual-troubleshooting) article. If operation is not as specified, go to next step.
  3. Install scan tool. With A/C on, monitor A/C REQUEST. If scan tool displays A/C REQUEST as YES, go to next step. If scan tool does not display A/C REQUEST as YES, go to step 8).
  4. Disconnect A/C compressor clutch harness connector. Connect a test light between harness connector terminals. If test light comes on, go to next step. If test light does not come on, go to step 12).
  5. Check for faulty A/C compressor clutch harness connections. If a problem is found, go to next step. If no problem is found, go to step 7).
  6. Repair faulty A/C compressor clutch wire harness connections. Go to step 27).
  7. Replace A/C compressor clutch. Go to step 27).
  8. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using a test light connected to ground, probe A/C request circuit (Dark Green/White wire) at VCM harness connector. If test light comes on, go to next step. If test light does not come on, go to step 11).
  9. Check for poor VCM harness connections. If a problem is found, go to next step. If no problem is found, go to step 26).
  10. Repair VCM harness connector. Go to step 27).
  11. Repair open or short to ground in Dark Green/White wire between VCM and A/C control switch. Go to step 27).
  12. Using a test light connected to ground, probe Dark Green wire at A/C compressor clutch harness connector. If test light comes on, go to next step. If test light does not come on, go to step 14).
  13. Repair open in A/C compressor clutch ground circuit (Black wire) between harness connector and ground. Go to step 27).
  14. Turn ignition on, engine off. Using scan tool, command A/C relay on. If A/C relay clicks, go to step 23). If A/C relay does not click, go to next step.
  15. Disconnect A/C relay. Using a test light connected to ground, probe A/C relay cavity No. 86 (Pink wire), then cavity No. 87 (Orange wire). If test light comes on for both wires, go to step 17). If test light does not come on for both wires, go to next step.
  16. Repair open or short to ground in affected circuit. Go to step 27).
  17. Connect a test light between A/C relay cavity No. 86 (Pink wire) and cavity No. 85 (Dark Green/White wire). Using scan tool, command A/C relay on. If test light comes on, go to next step. If test light does not come on, go to step 19).
  18. Replace A/C relay. Go to step 27).
  19. Check A/C relay control circuit (Dark Green/White wire) for faulty connection at VCM harness connector. If a problem is found, go to next step. If no problem is found, go to step 21).
  20. Repair faulty connection at VCM. Go to step 27).
  21. Check for open in Dark Green/White wire between VCM and A/C relay. If a problem is found, go to next step. If no problem is found, go to step 26).
  22. Repair open in Dark Green/White wire. Go to step 27).
  23. Remove A/C relay. Using a fused jumper wire, jumper A/C relay cavity No. 87 (Orange wire) and cavity No. 30 (Dark Green wire) together. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step 25).
  24. Replace A/C relay. Go to step 27).
  25. Repair open or short to ground in A/C compressor clutch control circuit (Dark Green wire). Go to step 27).
  26. Replace VCM. Go to next step.
  27. Using scan tool, select DTC CLEAR INFO. Start engine and allow it to reach normal operating temperature. Select DTC SPECIFIC, then enter DTC number that was set. Operate vehicle within conditions that may have set this DTC. If DTC does not reset, go to next step. If DTC resets, go to step 2).
  28. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any DTCs are displayed that have not been diagnosed, perform diagnosis for applicable DTC. See the TESTS W/CODES article in the ENGINE PERFORMANCE section. If no DTCs are displayed, system is okay.