Home ReviewsRefund
Home/Chevrolet/Malibu/Chevrolet Malibu V (1996-2000)/Repair manual/A/c Compressor/HVAC System Compressor Clutch Controls
Contents Wiring diagrams Section: A/c Compressor All sections

HVAC System Compressor Clutch Controls Chevrolet Malibu V

A/c Compressor 1 illustration ~2993 words

A/C COMPRESSOR CLUTCH CONTROLS

To provide improved idle quality, improved Wide Open Throttle (WOT) performance and A/C system protection, the compressor clutch is controlled by PCM.

For proper control of cooling fans, compressor clutch and Idle Air Control (IAC) valve, a refrigerant pressure sensor is used. PCM uses signal provided by sensor to monitor high and low side refrigerant pressures. If PCM detects a fault in refrigerant pressure circuit, compressor clutch will be disabled.

The A/C clutch relay is controlled by PCM. This allows PCM to raise idle speed before engaging compressor clutch, or disable compressor clutch during WOT, high engine RPM, high power steering loads and hot engine restarts. PCM also disables compressor clutch if coolant temperature becomes excessive.

Note. This article ONLY contains those testing procedures required to test A/C compressor clutch control circuit. 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 ENGINE PERFORMANCE section.

ApplicationLocation
Malibu & CutlassAt Right Rear Of Engine Compartment

A/C CLUTCH RELAY LOCATION

A/C CLUTCH CIRCUIT DIAGNOSIS

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. See WIRING DIAGRAMS .

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.

2.4L: MALIBU

Note. Body Function Controller (BFC) may also be known as Body Control Module (BCM).

Description

Powertrain Control Module (PCM) receives an A/C request signal from Body Function Controller (BFC) over CLASS 2 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 clutch relay is energized. PCM delays grounding relay circuit for .3 second. This allows PCM to adjust engine idle RPM for additional load.

PCM will temporarily de-energize A/C clutch relay for a hot engine restart, wide open throttle, if engine RPM is greater than 6000 RPM, or during Idle Air Control (IAC) valve reset. A/C clutch relay will remain de-energized when a DTC P0530 is set, or when there is no A/C request signal to PCM.

Diagnosis

  1. If On-Board Diagnostic (OBD) System Check has not been performed, see OBD SYSTEM CHECK in TESTS W/CODES article in ENGINE PERFORMANCE. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Install scan tool. Check if DTCs P0530, U1060 or U1064 are set. If one or more of these DTCs are set, see TESTS W/CODES article in ENGINE PERFORMANCE. If no DTCs are set, go to next step.
  3. Turn ignition on, engine off. If compressor clutch is engaged, go to next step. If compressor clutch is not engaged, go to step 5).
  4. Disconnect A/C clutch relay. If compressor clutch disengages, go to step 6). If compressor clutch does not disengage, go to step 7).
  5. Start engine and allow it to reach normal operating temperature. Cycle A/C on and off at control panel while observing scan tool. If scan tool indicates A/C is requested when A/C is on, go to step 16). If scan tool does not indicate as specified, go to step 12).
  6. Using a test light connected to battery voltage, probe A/C clutch relay control circuit terminal (Dark Green/White wire) at A/C clutch relay connector. If test light illuminates, go to step 8). If test light does not illuminate, go to step 9).
  7. Disconnect compressor clutch harness connector. If compressor clutch disengages, go to step 10). If compressor clutch does not disengage, go to step 11).
  8. Check A/C clutch relay control circuit (Dark Green/White wire) for a short to ground. Repair as necessary. Go to step 43). If no problem is found, go to step 34).
  9. Replace A/C clutch relay. Go to step 43).
  10. Repair compressor clutch battery feed circuit (Dark Green wire) for a short to power. Go to step 43).
  11. Replace faulty compressor clutch assembly. Go to step 43).
  12. Using scan tool, monitor Body Function Controller (BFC) serial data while commanding A/C selector switch on and off. If scan tool indicates a change when commanded on and off, go to step 35). If scan tool does not indicate a change, go to next step.
  13. Using a test light connected to ground, probe A/C selector switch input circuit (Light Green wire) at BFC harness connector. Cycle A/C selector switch on and off. If test light toggles on and off, go to next step. If test light does not toggle on and off, go to step 15).
  14. Diagnose BFC system circuits. See BODY CONTROL MODULE article in ACCESSORIES & ELECTRICAL. Go to step 43).
  15. Repair A/C request signal circuit (Light Green wire) between A/C heater control assembly and BFC. Go to step 43).
  16. Cycle A/C selector switch on and off. If compressor clutch cycles on and off, go to step 29). If compressor clutch does not cycle on and off, go to next step.
  17. Disconnect A/C clutch relay. Using a test light connected to ground, probe A/C clutch relay battery and ignition feed terminals at A/C clutch relay connector. If test light illuminates at both terminals, go to next step. If test light does not illuminate at both terminals, go to step 19).
  18. Connect a fused jumper wire between A/C clutch relay battery feed terminal and compressor clutch battery feed terminal. If compressor clutch engages, go to step 20). If compressor clutch does not engage, go to step 21).
  19. Check compressor clutch battery feed circuit (Dark/Green wire) for a short to ground. Also, check for an open in compressor clutch diode. Repair as necessary. Go to step 43). If no problem is found, go to step 22).
  20. Remove jumper wire. Start engine and let idle. Using a test light connected to battery voltage, probe A/C clutch relay control circuit terminal (Dark Green/White wire) at A/C clutch relay connector. Using scan tool, command relay on. If test light illuminates, go to step 9). If test light does not illuminate, go to step 23).
  21. Disconnect compressor clutch harness connector. Using a test light connected to ground, probe compressor clutch battery feed terminal (Dark Green wire). If test light illuminates, go to step 24). If test light does not illuminate, go to step 25).
  22. Repair open in battery or ignition feed circuit to A/C clutch relay. Go to step 43).
  23. Using a test light connected to ground, probe A/C clutch relay control circuit terminal (Dark Green/White wire) at A/C clutch relay connector. If test light illuminates, go to step 26). If test light does not illuminate, go to step 27).
  24. Using a test light connected to battery voltage, probe compressor clutch ground circuit terminal (Black wire). If test light illuminates, go to step 11). If test light does not illuminate, go to step 28).
  25. Repair open in compressor clutch battery feed circuit (Dark Green wire). Go to step 43).
  26. Check A/C clutch relay control circuit (Dark Green/White wire) for a short to power. Repair as necessary. Go to step 43). If no problem is found, go to step 34).
  27. Check A/C clutch relay control circuit (Dark Green/White wire) for an open or poor connection. Repair as necessary. Go to step 43). If no problem is found, go to step 34).
  28. Repair open or poor connection in compressor clutch ground circuit (Black wire). Go to step 43).
  29. Turn ignition on, engine off. Observe high-side pressure reading on scan tool. If reading is 40-430 psi (2.8-30.2 kg/cm 2 ), go to step 43). If reading is not as specified, go to next step.
  30. Disconnect A/C pressure sensor harness connector. Using a test light connected to battery voltage, probe A/C pressure sensor ground circuit terminal (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 33).
  31. Install A/C manifold gauge set. Turn ignition on, engine off. Compare high-side pressure reading on gauge with scan tool reading. If readings are within 20 psi (1.4 kg/cm 2 ) of each other, diagnose manual A/C-heater system. See «A/C-HEATER SYSTEM»(/chevrolet/malibu/v-1996-2000/remont/manual-hvac-system/#hvac-system-manual) article. If readings are not as specified, go to next step.
  32. Check A/C pressure sensor harness connector for a poor connection. Repair as necessary. If no problem is found, replace A/C pressure sensor. Go to step 43).
  33. Repair open or poor connection in A/C pressure sensor ground circuit (Black wire). Go to step 43).
  34. Replace PCM. Go to step 43).
  35. Turn ignition on, engine off. Observe high-side pressure reading on scan tool. If reading is 40-430 psi (2.8-30.2 kg/cm 2 ), diagnose BFC system circuits. See BODY CONTROL MODULE article in ACCESSORIES & ELECTRICAL. If reading is not as specified, go to next step.
  36. Install A/C manifold gauge set. Turn ignition on, engine off. Compare high-side pressure reading on gauge with scan tool reading. If readings are within 20 psi (1.4 kg/cm 2 ) of each other, diagnose manual A/C-heater system. See «A/C-HEATER SYSTEM»(/chevrolet/malibu/v-1996-2000/remont/manual-hvac-system/#hvac-system-manual) article. If readings are not as specified, go to next step.
  37. Disconnect A/C pressure sensor harness connector. If scan tool displays A/C high-side pressure as less than 421 psi (29.6 kg/cm 2 ), or one volt, go to next step. If scan tool display is not as specified, go to step 41).
  38. Using a DVOM connected to ground, probe A/C pressure sensor reference voltage circuit terminal (Gray wire). If reading is 5 volts, go to next step. If reading is not as specified, go to step 40).
  39. Connect a jumper wire between Gray wire and Red/Black wire of A/C pressure sensor harness connector. If scan tool displays A/C high-side pressure as greater than 421 psi (29.6 kg/cm 2 ), or 4.6 volts, go to step 32). If scan tool display is not as specified, go to step 42).
  40. Check A/C pressure sensor reference voltage circuit (Gray wire) for an open or poor connection. Repair as necessary. Go to step 43). If no problem is found, go to step 34).
  41. Check A/C pressure sensor signal circuit (Red/Black wire) for a short to power. Repair as necessary. Go to step 43). If no problem is found, go to step 34).
  42. Check A/C pressure sensor signal circuit (Red/Black wire) for an open, short to ground or poor connection. Repair as necessary. Go to next step. If no problem is found, go to step 34).
  43. Start engine and let idle. Cycle A/C selector on, then off. If compressor clutch cycles on, then off, system is okay at this time. See DIAGNOSTIC AIDS. If compressor clutch does not cycle as specified, go to step 2).

Diagnostic Aids

If DTCs P0530, U1016 or U1064 are set, diagnose them before proceeding. See TESTS W/CODES article in ENGINE PERFORMANCE. If the problem is insufficient cooling, check cooling fans for proper operation. See appropriate test in ENGINE COOLING FAN article. If cooling fans operate correctly, diagnose manual A/C-heater system. See A/C-HEATER SYSTEM article.

A/C refrigerant pressure less than 43 psi (3.0 kg/cm 2 ), or greater than 428 psi (30.1 kg/cm 2 ) will cause PCM to disable compressor clutch. With engine running and A/C on, use scan tool to monitor A/C high-side system pressure for 2 minutes. If pressure goes out of range, diagnose A/C-heater system.

3.1L: CUTLASS & MALIBU

Note. Body Function Controller (BFC) may also be known as Body Control Module (BCM).

When A/C is selected through A/C control panel, a 12-volt signal is supplied to A/C request input terminal of PCM. A/C clutch relay is controlled through PCM which also monitors A/C refrigerant pressure. If A/C refrigerant pressure and engine operating conditions are within a specific calibrated acceptable range, PCM will enable A/C clutch relay. This is accomplished by providing a ground path for A/C clutch relay coil with PCM. When A/C clutch relay is enabled, battery voltage is supplied to compressor clutch coil.

PCM will enable compressor clutch whenever engine is running and A/C has been requested, unless

  1. Throttle angle is greater than 90 percent.
  2. A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ).
  3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ).
  4. Ignition voltage is less than 10.5 volts.
  5. Engine speed is greater than 4500 RPM for 5 seconds.
  6. Engine coolant temperature is greater than 257°F (125°C).
  7. Intake air temperature is less than 41°F (5°C).
  1. If On-Board Diagnostic (OBD) System Check has not been performed, see OBD SYSTEM CHECK in TESTS W/CODES article in ENGINE PERFORMANCE. If OBD SYSTEM CHECK has been performed, go to next step.
  2. Install scan tool. Check if any DTCs are set. If any DTCs are set, perform diagnosis for DTCs first. See TESTS W/CODES article in ENGINE PERFORMANCE. If no DTCs are set, go to next step.
  3. Ensure ambient air temperature is greater than 41°F (5°C), A/C pressure is greater than 35 psi (2.5 kg/cm 2 ) (.40 volt on scan tool), and coolant temperature is less than 250°F (121°C). Turn A/C off. Turn ignition on, engine off. Listen for engagement of compressor clutch. If compressor clutch engages, go to step 18). If compressor clutch does not engage, go to next step.
  4. With engine running at idle, select DEFROST or MAX mode. Observe compressor clutch. If compressor clutch is engaged, problem may be intermittent. If compressor clutch is not engaged, go to next step.
  5. With DEFROST or MAX mode selected, monitor A/C REQUEST display on scan tool engine data list. If A/C REQUEST displays YES, go to step 9). If A/C REQUEST does not display YES, go to next step.
  6. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. With DEFROST or MAX mode selected, use a DVOM and measure voltage on A/C request circuit at PCM harness connector. If battery voltage is present, go to step 8). If battery voltage is not present, go to next step.
  7. Check A/C request circuit for an open, short to ground or poor connection at A/C control head/programmer. Repair as necessary. Go to step 29). If no problem is found, diagnose A/C controls. See «A/C-HEATER SYSTEM»(/chevrolet/malibu/v-1996-2000/remont/manual-hvac-system/#hvac-system-manual) article.
  8. Check A/C request circuit for a poor connection at PCM. Repair as necessary. Go to step 29). If no problem is found, go to step 27).
  9. Observe A/C refrigerant pressure display on scan tool. If pressure is 36-440 psi (2.5-30.9 kg/cm 2 ), go to step 12). If pressure is not as specified, go to next step.
  10. Install A/C manifold gauge set. Observe high-side refrigerant pressure. If pressure is 36-440 psi (2.5-30 kg/cm 2 ), go to next step. If pressure is not as specified, charge A/C system using approved A/C refrigerant recovery/recycling equipment. Go to step 29).
  11. Turn ignition off. Disconnect A/C pressure sensor. Turn ignition on. View A/C HIGH-SIDE display on scan tool engine data list. If scan tool displays A/C high-side pressure as 0 psi (0 kg/cm 2 ), go to step 28). If scan tool does not display A/C high-side pressure as specified, go to step 27).
  12. Disconnect A/C clutch relay. Using a test light connected to ground, probe both ignition feed circuit terminals (Pink wires) at A/C clutch relay harness connector. If test light illuminates at both terminals, go to next step. If test light does not illuminate at both terminals, go to step 23).
  13. Connect a fused jumper wire between one ignition feed circuit (Pink wire) and compressor clutch battery feed circuit (Dark Green wire) at A/C clutch relay harness connector. If compressor clutch engages, go to next step. If compressor clutch does not engage, leave jumper wire in place and go to step 15).
  14. Check for poor connections at A/C clutch relay. Repair as necessary. Go to step 29). If no problem is found, go to step 24).
  15. Disconnect compressor clutch harness connector. Connect a test light between compressor clutch battery feed circuit (Dark Green wire) and compressor clutch ground circuit (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
  16. Check for poor connections at compressor clutch. Repair as necessary. Go to step 29). If no problem is found, go to step 25).
  17. Check for an open or short to ground in compressor clutch battery feed circuit (Dark Green wire). Repair as necessary. Go to step 29). If no problem is found, go to step 26).
  18. Turn ignition on, A/C off. Observe A/C REQUEST display on scan tool. If A/C REQUEST displays YES, go to next step. If A/C REQUEST does not display YES, go to step 21).
  19. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on, A/C off. Using a DVOM, measure voltage between ground and A/C request circuit at PCM harness connector. If reading is near battery voltage, go to next step. If reading is not as specified, go to step 27).
  20. Turn ignition off. Disconnect Body Function Controller (BFC). Turn ignition on. Check A/C request circuit for a short to power. Repair as necessary. Go to step 29). If no problem is found, diagnose A/C controls. See «A/C-HEATER SYSTEM»(/chevrolet/malibu/v-1996-2000/remont/manual-hvac-system/#hvac-system-manual) article.
  21. Disconnect A/C clutch relay. Start engine and observe compressor clutch. If compressor clutch is engaged, go to next step. If compressor clutch is not engaged, go to step 24).
  22. Locate and repair short to power in compressor clutch battery feed circuit (Dark Green wire). Go to step 29).
  23. Repair open or short to ground in A/C clutch relay ignition feed circuit (Pink wire). Go to step 29).
  24. Replace A/C clutch relay. Go to step 29).
  25. Replace compressor clutch coil. Go to step 29).
  26. Locate and repair open in compressor clutch ground circuit (Black wire). Go to step 29).
  27. Replace PCM. Go to step 29).
  28. Replace A/C pressure sensor. Go to next step.
  29. Ensure ambient air temperature is greater than 41°F (5°C), A/C pressure is greater than 96°F (36°C), and coolant temperature is less than 250°F (121°C). Start engine and let idle. Turn A/C on. Listen for engagement of compressor clutch. If compressor clutch engages, system is okay. If compressor clutch does not engage, go to step 3).

A/C Compressor Clutch Control Circuit Wiring Diagram. Scheme 1

Scheme 1: A/C Compressor Clutch Control Circuit Wiring Diagram
Scheme 1: A/C Compressor Clutch Control Circuit Wiring Diagram