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A/c Compressor Clutch Controls Chevrolet Blazer S15

A/c Compressor 1 illustration ~2232 words

DESCRIPTION & OPERATION

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.

TROUBLE SHOOTING

Note. This article contains testing that is part of General Motors Computerized Engine Controls. Only testing required to test A/C compressor clutch control 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 appropriate article in the ENGINE PERFORMANCE Section.

RELAY LOCATION

ApplicationLocation
2.2L(1) On Bracket, On Left Side Of Firewall
(1) (Scheme 1)

A/C COMPRESSOR CLUTCH RELAY LOCATION

Scheme 1

Scheme 1
Scheme 1

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 (TK O-A) and Cartridge Kit (7000001), Tech 1 OBD II Vehicle Interface Module Kit (7000041), or other 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.

Description

PCM receives an A/C request signal from Instrument Panel Cluster (IPC) over serial data line. When A/C is requested, PCM provides a ground path to A/C clutch relay control circuit. When relay circuit is grounded, A/C compressor clutch relay is energized. After A/C request has been selected, PCM will delay grounding A/C compressor relay control circuit for .3 second. This allows PCM to adjust engine idle RPM for additional load.

PCM will temporarily de-energize A/C compressor clutch relay for a hot engine restart, wide open throttle, engine speed greater than 6000 RPM, or Idle Air Control (IAC) valve reset. A/C compressor clutch relay will remain de-energized when a Diagnostic Trouble Code (DTC) P0530 is set or there is no A/C request signal due to an open A/C select switch circuit.

Compressor Clutch Control Circuit Diagnosis

  1. If On-Board Diagnostic (OBD) System Check has not been performed, see appropriate ENGINE PERFORMANCE article in ENGINE PERFORMANCE section and go to OBD SYSTEM CHECK. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Turn ignition on, engine off. Check A/C compressor clutch to see if it is engaged. If compressor clutch is engaged, go to next step. If compressor clutch is not engaged, go to step 4).
  3. Disconnect A/C relay. With a test light connected to voltage, probe A/C relay control circuit (Dark Green/White wire). If test light comes on, go to step 12). If test light does not come on, go to step 13).
  4. Start and run engine until it reaches normal operating temperature. Cycle A/C on and off using instrument panel control. If A/C compressor clutch cycles on and off, see DIAGNOSTIC AIDS. If A/C compressor clutch does not cycle on and off, go to next step.
  5. Install scan tester. Turn A/C on using instrument panel control. Select A/C REQUEST parameter on scan tester. If A/C REQUEST reads YES, go to step 7). If A/C REQUEST does not read YES, go to next step.
  6. Using a scan tester, select body applications IPC data list. Select A/C REQUEST parameter. If A/C REQUEST reads YES on scan tester, go to step 14). If A/C REQUEST does not read YES on scan tester, go to step 15).
  7. Start engine. Turn A/C on. Select A/C HIGH SIDE parameter on scan tester. If A/C HIGH SIDE value is between 40-430 psi (2.8-30.2 kg/cm 2 ), go to step 9). If A/C HIGH SIDE value is not between 40-430 psi (2.8-30.2 kg/cm 2 ), go to next step.
  8. Install an A/C manifold gauge set. Observe pressures on manifold gauge set and scan tester. If high side pressures are within 20 psi (1.4 kg/cm 2 ) of each other, see «A/C-HEATER SYSTEM - MANUAL»(/chevrolet/blazer/s15-1994-1998/remont/manual-hvac-system/#hvac-system-manual) article. If high side pressures are not within 20 psi (1.4 kg/cm 2 ) of each other, go to step 16).
  9. Disconnect A/C relay. With a test light connected to ground probe terminals No. 85 (Dark Green/White wire) and 30 (Dark Green wire). If test light lights on both terminals, go to step 10). If test light does not light on both terminals, go to step 17).
  10. Turn ignition on. Turn A/C on. Jumper terminals No. 30 (Dark Green wire) and 87 (Orange wire) together. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step 18).
  11. Turn ignition on, engine off. Turn A/C on. With a test light connected to voltage, probe A/C relay control circuit (Dark Green/White wire). If test light comes on, go to step 19). If test light does not come on, go to step 20).
  12. Check A/C relay control circuit (Dark Green/White wire) for a short to ground. If a short to ground was found, go to step 21). If a short to ground was not found, go to step 14).
  13. Check A/C relay control circuit (Dark Green/White wire) for a short to voltage. If a repair was made, go to step 21). If a repair was not made, go to step 19).
  14. Replace PCM.
  15. Check AC COMP fuse No. 14 (10-amp). If blown, replace and check for a short to ground in A/C request circuit. If fuse is okay, check for an open in A/C request switch or circuit. Go to step 21).
  16. Replace A/C refrigerant pressure sensor. Go to step 21).
  17. Repair open in circuit that did not illuminate test light.
  18. Check for an open in circuit between terminal No. 87 (Orange wire) of A/C compressor clutch relay and connector "B" of A/C compressor clutch (Black wire), or an open ground circuit to compressor clutch or a faulty compressor clutch. Go to step 21).
  19. Replace A/C compressor clutch relay. Go to step 21).
  20. Check for an open in A/C relay control circuit (Dark Green/White wire). If relay control circuit is okay, go to next step.
  21. Operate vehicle within those conditions under which original symptom was noted. If system does not operate correctly, system is okay. If system does not operate correctly, go to Diagnostic Aids.

Diagnostic Aids

If complaint is insufficient cooling, problem may be caused by an inoperative cooling fan. An A/C pressure is outside range of 43-428 psi (3-30 kg/cm 2 ), A/C compressor clutch will be disabled by PCM. Observe A/C refrigerant pressure parameter on scan tester for 2 minutes with engine idling and A/C on. If pressure goes out of range, see A/C-HEATER SYSTEM - MANUAL article.

Vehicle Control Module (VCM) control of A/C clutch improves idle quality and performance by delaying clutch engagement until idle speed is increased, releasing clutch when idle speed is too low, and smooths cycling of compressor by providing additional fuel the instant clutch is applied.

Turning on A/C supplies battery voltage through pressure switches to VCM. When VCM receives voltage on A/C request signal, A/C enable relay circuit will be grounded. A/C compressor clutch will then engage.

  1. Before performing diagnosis ensure A/C system is adequately charged. If system is not adequately charged, evacuate and recharge system. If system is adequately charged, go to next step.
  2. Start and run engine until is reaches normal operating temperature. Run engine at idle. Turn A/C on and off. If A/C clutch engages and disengages within 20 seconds, system is now operating properly. If A/C clutch does not engage and disengage within 20 seconds, go to step 3).
  3. Connect scan tester. Turn A/C on. Monitor A/C REQUEST in data stream. If display reads YES, go to next step. If display does not read YES, go to step 8).
  4. Disconnect compressor clutch connector. Connect voltmeter between A/C clutch signal circuit (Dark Green wire) and ground circuit of A/C compressor clutch harness connector (Black wire). If battery voltage is present, go to next step. If battery voltage is not present, go to step 12).
  5. Check for a faulty compressor clutch harness connector. If a repair was made, go to next step. If a repair was not made, go to step 7).
  6. Repair A/C compressor clutch harness connector. Go to step 37).
  7. Replace A/C compressor clutch. Go to step 37).
  8. Turn ignition off. Disconnect Gray VCM connector. Turn ignition on. Connect voltmeter to VCM harness connector terminal GR25 (Dark Green/White wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 11).
  9. Check for poor connection at Gray VCM harness connector. If a poor connection is present, go to next step. If a poor connection is not present, go to step 36).
  10. Repair VCM harness connector. Go to step 37).
  11. Repair open or short to ground in Dark Green/White wire to A/C pressure switch and/or A/C control switch. Go to step 37).
  12. Connect voltmeter to A/C clutch signal circuit (Dark Green wire) of A/C clutch harness connector and engine ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14).
  13. Repair ground circuit of A/C clutch harness connector (Black wire). Go to step 37).
  14. Install scan tester. Turn ignition on, engine off. Using OUTPUT TEST function of scan tester, 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. Connect voltmeter between terminal No. 85 (Pink wire) of relay harness connector and ground. If battery voltage is present, go to step 17). If battery voltage is not present, go to next step.
  16. Repair open or short to ground in harness connector terminal No. 85 (Pink wire). Go to step 37).
  17. Connect voltmeter between A/C relay harness connector terminals No. 85 (Pink wire) and 86 (Dark Green/White wire). Install scan tester. Using OUTPUT TEST function of scan tester, command A/C relay on. If battery voltage is present, go to next step. If battery voltage is not present, go to step 19).
  18. Replace A/C relay. Go to step 37.
  19. Check for a faulty connection at Gray VCM harness connector. If a repair was made, go to next step. If a repair was not made, go to step 21).
  20. Repair Gray VCM connector. Go to step 37).
  21. Check for an open circuit between A/C relay harness connector terminal No. 86 (Dark Green/White wire) and Gray VCM connector terminal RE9 (Dark Green/White wire). If a problem was found, go to next step. If a problem was not found, go to step 36).
  22. Repair open in circuit between A/C relay harness connector terminal No. 86 (Dark Green/White wire) and Gray VCM connector terminal RE9 (Dark Green/White wire). Go to step 37).
  23. Remove A/C relay. Connect voltmeter between A/C relay harness connector terminal No. 30 (Orange wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 29).
  24. Reconnect A/C relay. Disconnect A/C high pressure switch. Connect voltmeter between A/C high pressure switch harness connector (Dark Green wire) and ground. If battery voltage is present, go to step 34). If battery voltage is not present, go to next step.
  25. Check for an open in circuit between A/C relay harness connector terminal No. 87 (Dark Green wire) and A/C high pressure switch harness connector. If a problem was found, go to next step. If a problem was not found, go to step 27).
  26. Repair open in circuit between A/C relay harness connector terminal No. 87 (Dark Green wire) and A/C high pressure switch harness connector. Go to step 37).
  27. Replace A/C relay. Go to step 37).
  28. Disconnect low pressure switch. Connect voltmeter between low pressure switch harness Light Green wire and ground. If about battery voltage is present, go to step 30). If about battery voltage is not present, go to next step.
  29. Repair open circuit to low pressure switch harness connector Light Green wire. Go to step 37).
  30. Connect a jumper wire between low pressure switch harness connector. Connect voltmeter between A/C relay harness connector terminal No. 30 (Orange wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 32).
  31. Replace A/C low pressure switch. Go to step 37).
  32. Repair open circuit between low pressure switch harness connector and A/C relay harness connector terminal No. 30 (Orange wire). Go to step 37).
  33. Connect a jumper wire between high pressure switch connector. Check for battery voltage at A/C compressor clutch connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 35).
  34. Replace high pressure switch. Go to step 37).
  35. Repair open in A/C clutch signal circuit (Dark Green/White wire). Go to step 37).
  36. Replace VCM. Go to step 37).
  37. Using scan tester, select DTC CLEAR INFO. Start and idle engine until it reaches normal operating temperature. Select DTC SPECIFIC, then enter DTC number that was set. Operate vehicle within conditions that may have set this DTC in the first place. If DTC does not reset, go to next step. If DTC resets, go to step 2).
  38. Using scan tester, select CAPTURE INFO, REVIEW INFO. If any DTCs are displayed that have not been diagnosed, perform diagnosis for applicable DTC. See appropriate ENGINE PERFORMANCE article in ENGINE PERFORMANCE section.