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Home >> Isuzu >> 2002 >> Axiom Base, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Miscellaneous Powertrain Control Module Controls >> A/C Clutch Control (Axiom & Trooper) >> Diagnostic Procedure
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Diagnostic Procedure

  1. Perform On-Board Diagnostics II (OBD-II) System Check. See ON-BOARD DIAGNOSTICS II (OBD-II) SYSTEM CHECK under SELF-DIAGNOSTICS in appropriate SELF-DIAGNOSTICS article. After performing OBD-II system check, go to next step.
  2. If any DTCs were stored in memory, perform appropriate test before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no DTCs were stored, go to next step.
  3. Disconnect A/C pressure switch harness connector. Pressure switch is located on receiver/drier behind left side of grill. Using DVOM check continuity of A/C pressure switch. If continuity does not exist, repair cause of open. For testing procedure, see appropriate AIR CONDITIONING & HEATINGarticle. If continuity exists, go to next step.
    4. NOTE: Before continuing testing, ensure that intake air temperature is 60°F (15°C) or more, and engine coolant temperature is less than 246°F (119°C).
  4. Ensure A/C is switched off. Start engine and allow to idle for at least one minute. Observe A/C compressor clutch. If A/C compressor clutch is engaged even though switch is off, go to step  37. If A/C compressor clutch is not engaged, leave engine running with A/C on and go to next step.
  5. Turn A/C and blower on. Observe A/C compressor clutch. If A/C compressor clutch engages, check for intermittent problem. See DIAGNOSTIC AIDS . If A/C compressor clutch does not engage, leave engine running and go to next step.
  6. On scan tool, select MISCELLANEOUS TESTS, and then RELAYS test. If A/C REQUEST display indicates YES, go to step  26. If scan tool does not display as specified, go to next step.
  7. Temporarily switch A/C compressor and A/C thermostat relays. Relays are located in underhood fuse/relay box. Repeat test starting in step  5. If A/C REQUEST display now indicates YES, go to next step. If scan tool still does not display as specified, go to step  9.
  8. Replace original A/C thermostat relay. After repair, retest system.
  9. Turn A/C blower on. If blower operates, go to next step. If blower does not operate, go to step  11.
  10. Repair or replace blower as necessary. See appropriate A/C-HEATER SYSTEMSarticle. After repair, retest system.
  11. Check for blown A/C fuses. On Axiom, Passport, Rodeo and Rodeo Sport, fuses are located in underhood fuse/relay box. On Trooper, fuses are located in dash fuse/relay box. If fuses are okay, go to step  13. If fuses are blown, go to next step.
  12. Check for and repair open in circuit between fuses and A/C pressure switch. See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. Replace any blown fuses. After repair, retest system.
  13. Remove glove box to gain access to A/C electronic thermostat harness connector. See Fig 1. Disconnect A/C thermostat 2-pin harness connector. Using a fused jumper, jumper between ground and A/C electronic thermostat signal circuit (Yellow/Blue wire on Axiom; Light Green/White wire on Trooper). Turn A/C and blower on. On scan tool, observe A/C REQUEST display. If display indicates YES, go to next step. If display does not indicate YES, go to step  17.
  14. Turn ignition on. Using DVOM, measure voltage between ground and A/C electronic thermostat signal circuit (Yellow/Blue wire on Axiom; Light Green/White wire on Trooper). Turn A/C and blower on. If battery voltage exists, go to step  17. If battery voltage does not exist, go to next step.
  15. Check for open in A/C electronic thermostat signal circuit between thermostat and A/C switch. See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. If problem is found, go to next step. If no problem is found, go to step  17.
  16. Repair open in A/C electronic thermostat signal circuit. After repair, retest system.
  17. Check for open in signal circuit between A/C thermostat relay and PCM A/C request terminal. See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. If problem is found, go to next step. If no problem is found, go to step  19.
  18. Repair open in signal circuit between A/C thermostat relay and PCM A/C request terminal. After repair, retest system.
  19. Turn ignition on. Measure voltage between ground and A/C pressure switch harness connector terminal No. 2 (Brown wire). See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. If battery voltage exists, go to step  21. If battery voltage does not exist, go to next step.
  20. Repair open in Brown wire (pressure switch voltage supply) between A/C fuse and pressure switch. After repair, retest system.
  21. Check for open in Brown wire (pressure switch voltage supply) between A/C fuse and pressure switch. If problem is found, go to next step. If no problem is found, go to step  23.
  22. Repair open in Brown wire (pressure switch voltage supply) between A/C fuse and pressure switch. After repair, retest system.
  23. Check for poor, loose or damage terminal connections in PCM harness connector. If problem is found, go to next step. If no problem is found, go to step  25.
  24. Repair or replace suspect PCM harness connector terminal(s). After repair, retest system.
  25. Replace and reprogram PCM. See POWERTRAIN CONTROL MODULE REPLACEMENT under POWERTRAIN CONTROL MODULE in appropriate SELF-DIAGNOSTICS article. After repair, repeat OBD-II system check. See ON-BOARD DIAGNOSTIC II SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
  26. Remove A/C compressor relay from underhood relay. Turn ignition on. Using DVOM measure voltage between ground and A/C compressor relay socket cavities No. 2 and 5 (Brown wires at both cavities). If battery voltage exists, leave relay disconnected and go to step  28. If battery voltage does not exist, go to next step.
  27. Repair open or short in Brown wire (A/C compressor relay voltage supply) between A/C fuse and A/C compressor relay. After repair, retest system.
  28. Start engine. Turn A/C and blower on. Measure voltage between ground and A/C compressor relay socket cavity No. 4 (Gray/Red wire). If battery voltage exists, leave relay disconnected and go to step  32. If battery voltage does not exist, go to next step.
  29. Check for open in Gray/Red wire (relay control circuit) between PCM and A/C compressor relay. If problem is found, go to next step. If no problem is found, go to step  31.
  30. Repair open in Gray/Red wire (relay control circuit) between PCM and A/C compressor relay. After repair, retest system.
  31. Check for poor, loose or damage terminal connections in PCM harness connector. If problem is found, go to step  24. If no problem is found, go to step  25.
  32. Connect a fused jumper between A/C compressor relay socket cavities No. 1 and 5. Start engine. Turn A/C and blower on. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step  34.
  33. Repair A/C compressor clutch as necessary. After repair, retest system.
  34. Check for open in Brown/Yellow wire between A/C compressor relay and A/C compressor clutch. See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. If problem is found, go to next step. If no problem is found, go to step  36.
  35. Repair open in Brown/Yellow wire between A/C compressor relay and A/C compressor clutch. After repair, retest system.
  36. Service compressor clutch or replace compressor due to a faulty internal overheat switch. After repair, retest system.
  37. Remove A/C compressor relay from underhood fuse/relay box. Ensure A/C is turned off. Start engine. If A/C compressor clutch is engaged even though A/C is turned off and relay has been removed, go to next step. If A/C compressor clutch does not engage, go to step  39.
  38. Repair short to voltage in Brown/Yellow wire between A/C compressor relay and A/C compressor clutch. After repair, retest system.
  39. Turn ignition off. Install A/C compressor relay. Disconnect A/C thermostat relay from underhood fuse/relay box. Start engine. If A/C compressor clutch is engaged even though A/C is turned off and relay has been removed, go to next step. If A/C compressor clutch does not engage, go to step  42.
  40. Check for short to ground in Gray/Red wire between PCM and A/C compressor relay. See WIRING DIAGRAMS in appropriate A/C-HEATER SYSTEMSarticle. If problem is found, go to next step. If no problem is found, go to step  25.
  41. Repair short to ground in Gray/Red wire between PCM and A/C compressor relay. After repair, retest system.
  42. Repair short to ground in circuits between A/C thermostat relay and electronic thermostat. After repair, retest system.
Fig 1: Locating A/C Electronic Thermostat Harness Connector
G00141544Courtesy of ISUZU MOTOR CO.
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