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HVAC System Compressor Clutch Controls Buick Riviera VIII

A/c Compressor ~2615 words

DESCRIPTION & OPERATION

To improve idle quality and Wide Open Throttle (WOT) performance, and for system protection, the A/C compressor clutch is controlled by the Powertrain Control Module (PCM).

A refrigerant pressure sensor is used to indicate high and low side refrigerant pressure to the PCM for controlling cooling fan, A/C compressor clutch and Idle Air Control (IAC) valve. If a fault is detected in refrigerant pressure circuit, A/C compressor clutch will be disabled.

The A/C compressor clutch relay is controlled by the PCM. This allows the PCM to raise idle speed before engaging compressor clutch, and 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.

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
All ModelsIn Underhood Fuse/Relay Block, On Right Front Of Engine Compartment

A/C COMPRESSOR CLUTCH RELAY LOCATION

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

When A/C is selected a 12-volt signal is supplied to A/C request input of PCM. A/C compressor clutch relay is controlled through PCM. PCM 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 compressor relay. This is done by providing a ground path for A/C relay coil within PCM. When A/C compressor relay is enabled, battery voltage is supplied to compressor clutch coil.

PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless throttle is greater than 90 percent, A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ) or 4.27 volts, or less than 34 psi (2.3 kg/cm 2 ), or .35 volt as determined by A/C refrigerant pressure sensor, ignition voltage less than 10.5 volts, engine speed greater than 4500 RPM for 5 seconds, engine coolant temperature greater than 257°F (125°C), and intake air temperature less than 41°F (5°C).

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. Check if any PCM or Heating, Ventilation or A/C (HVAC) Diagnostic Trouble Codes (DTCs) have been set. If any DTCs are set, perform diagnosis for that code first. See appropriate ENGINE PERFORMANCE article in ENGINE PERFORMANCE section and go to OBD SYSTEM CHECK. If no DTCs are set, go to next step.
  3. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). Turn A/C off. Start and idle engine. Observe A/C compressor. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
  4. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on A/C control head. Observe A/C compressor. If A/C compressor clutch is engaged, system is operating correctly. Problem may be intermittent. If A/C compressor clutch is not engaged, go to next step.
  5. With DEFROST or MAX mode still selected, observe A/C REQUEST display on scan tester. 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. Turn ignition on. With DEFROST or MAX mode still selected, measure voltage on A/C request circuit at PCM harness connector (Dark Green/White wire). If about 12 volts are present, go to step 8). If about 12 volts are not present, go to next step.
  7. Check A/C request circuit (Dark Green/White wire) for an open, short to ground, or poor connection at A/C control head. If a problem was found, diagnose A/C control. See article, «A/C-HEATER SYSTEM - AUTOMATIC»(/buick/riviera/viii-1994-1999/remont/automatic-hvac-system/#hvac-system-automatic) . If a problem is not found, go to step 37).
  8. Check A/C request circuit (Dark Green/White wire) for a poor connection at PCM. If a repair was made, go to step 37). If a repair was not made, go to step 35).
  9. Observe A/C refrigerant pressure sensor display on scan tester. If indicated pressure is .35-4.27 volts, go to step 12). If indicated pressure is not .35-4.27 volts, go to next step.
  10. Connect Manifold Gauge Set (J 39183-C). Observe high side refrigerant pressure on gauge. If high side refrigerant pressure is within 34-414 psi (2.3-29 kg/cm 2 ), go to next step. If high side refrigerant pressure is not within 34-414 psi (2.3-29 kg/cm 2 ), charge A/C system.
  11. Turn ignition off. Disconnect PCM and A/C refrigerant pressure sensor. Measure resistance of following circuits between PCM and A/C refrigerant pressure sensor: Refrigerant pressure sensor signal circuit (Red/Black wire). 5-volt reference "B" circuit (Gray wire). Sensor ground circuit (Black wire). If any resistance is higher than 5 ohms, locate and repair cause of high resistance in circuit as necessary, then go to step 37). If any resistance is not higher than 5 ohms, go to step 18).
  12. Disconnect A/C relay electrical connector. Probe ignition feed circuits (Orange and Dark Green wires) at A/C relay harness connector with a test light to ground. If test light comes on, go to next step. If test light does not come on, go to step 31).
  13. Connect a fused jumper between ignition feed circuit and A/C compressor clutch control circuit (Dark Green wire) at A/C relay connector. If A/C compressor clutch engages, go to step 14). If A/C compressor clutch does not engage, go to step 15).
  14. Check for poor connections at A/C relay. If a repair was made, go to step 37). If a repair was not made, go to step 32).
  15. Disconnect A/C compressor clutch electrical connector (leave ignition feed circuit and A/C compressor clutch control circuit jumpered at A/C relay connector). Connect a test light between A/C compressor clutch control circuit (Dark Green wire) and compressor ground circuit (Black wire). If test light comes on, go to next step. If test light does not come on, go to step 17).
  16. Check for poor connections at A/C compressor clutch. If a repair was made, go to step 37). If a repair was not made, go to step 33).
  17. Check for an open or short to ground in A/C compressor clutch control circuit (Dark Green wire). If a repair was made, go to step 37). If a repair was not made, go to step 34).
  18. Leave PCM and A/C refrigerant pressure sensor disconnected at PCM. Turn ignition on. Measure voltage between A/C refrigerant pressure signal circuit (Red/Black wire) and ground. If voltage is about zero volts, go to next step. If voltage is not about zero volts, go to step 20).
  19. Check the following: 5-volt reference "B" circuit (Gray wire) for a poor connection at PCM. 5-volt reference "B" circuit (Gray wire) for a poor connection at refrigerant pressure sensor. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at PCM. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at refrigerant pressure sensor. Sensor ground circuit (Black wire) for a poor connection at refrigerant pressure sensor. If a problem is found, repair as necessary and go to step 37). If a problem was not found, go to step 36).
  20. Locate and repair short to voltage in A/C refrigerant pressure signal circuit (Red/Black wire). Go to step 37).
  21. Turn ignition on. Turn A/C off. Observe A/C REQUEST on scan tester. If A/C REQUEST displays YES, go to next step. If A/C REQUEST does not display YES, go to step 24).
  22. Turn ignition off. Disconnect PCM. Turn ignition on, A/C off. Measure voltage between A/C request circuit (Dark Green/White wire) at PCM harness connector and ground. If voltage measures near battery voltage, go to next step. If voltage does not measure near battery voltage, go to step 35).
  23. Turn ignition off. Disconnect A/C control head/programmer. Turn ignition on. Check A/C request circuit (Dark Green/White wire) for a short to voltage. If a problem was found and a repair was made, go to step 37). If a problem was not found, diagnose A/C controls. See appropriate «A/C-HEATER SYSTEM - AUTOMATIC»(/buick/riviera/viii-1994-1999/remont/automatic-hvac-system/#hvac-system-automatic) article.
  24. Disconnect A/C relay. Start vehicle and observe A/C compressor. If A/C compressor clutch is engaged, go to step 29). If A/C compressor clutch is not engaged, go to next step.
  25. Probe A/C compressor clutch control circuit (Dark Green wire) at A/C relay harness connector with a test light to ground. If test light comes on, go to step 27). If test light does not come on, go to next step.
  26. Replace A/C relay. Go to step 37).
  27. Turn ignition off. Disconnect PCM. Probe A/C relay driver circuit (Dark Green/White wire) at PCM connector with a test light connected to battery voltage. If test light comes on, go to next step. If test light does not come on, go to step 35).
  28. Repair short to ground in A/C compressor clutch relay driver circuit (Dark Green/White wire). Go to step 37).
  29. Turn ignition off. Disconnect A/C compressor clutch electrical connector. Start engine and observe A/C compressor. If A/C compressor clutch is engaged, go to step 33). If A/C compressor clutch is not engaged, go to next step.
  30. Locate and repair short to voltage in A/C compressor clutch control circuit (Dark Green wire). Go to step 37).
  31. Repair open or short to ground in ignition feed circuit (Pink wire) to A/C compressor relay. Go to step 37).
  32. Replace A/C compressor relay. Go to step 37).
  33. Repair A/C compressor clutch. See COMPRESSOR SERVICING article in. Go to step 37).
  34. Locate and repair open in A/C compressor clutch ground circuit (Black wire). Go to step 37).
  35. Replace PCM. Go to step 37).
  36. Replace A/C refrigerant pressure sensor. Go to step 37).
  37. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). With A/C off, start and idle engine. Observe A/C compressor. If clutch is engaged, go to step 21). If clutch is not engaged, go to next step.
  38. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on control head. Observe A/C compressor. If A/C compressor clutch is engaged, system is okay. If A/C compressor clutch is not engaged, go to step 5).

System consists of an A/C control head, A/C refrigerant high and low pressure switches, A/C high and low temperature sensors, a control relay, compressor clutch and PCM.

When A/C control head is placed in A/C mode, request signal is sent to PCM. PCM will then energize A/C clutch relay, unless abnormally high or low A/C pressure is detected by A/C refrigerant pressure switches. PCM also monitors A/C low temperature sensors to cycle A/C clutch on and off. If PCM detects an A/C evaporator temperature less than 36°F (2°C), A/C clutch will be prohibited from being enabled. PCM will also energize cooling fans on when A/C is requested.

  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. Check if any Diagnostic Trouble Codes (DTCs) are stored. If any DTCs are set, perform diagnosis for codes first. See appropriate ENGINE PERFORMANCE article in ENGINE PERFORMANCE section and go to OBD SYSTEM CHECK. If no DTCs are set, go to next step.
  3. Ensure ambient temperature is greater than -10°F (-23°C). With A/C off, start and idle engine. Observe A/C compressor clutch. If compressor clutch is engaged, go to step 10). If clutch is not engaged, go to step 4).
  4. With engine idling and A/C on for more than 30 seconds, check compressor clutch. If compressor clutch is engaged, system is okay. If clutch is not engaged, go to next step.
  5. Turn ignition off. Connect scan tester. Turn ignition on. With A/C still on, observe A/C relay control circuit in ENGINE 3 DATA VALUES. If scan tester displays OKAY, go to next step. If scan tester does not display OKAY, go to step 12).
  6. Remove A/C relay. With a test light connected to ground, check terminals No. 30 (Pink wire) and 85 (Pink wire) in A/C relay cavity. If test light lights on both terminals, go to next step. If test light does not light on both terminals, go to step 14).
  7. With a fused jumper wire, connect terminal No. 30 (Pink wire) and 87 (Dark Green wire) in A/C relay cavity. Observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 15). If A/C compressor clutch is not engaged, go to next step.
  8. Disconnect A/C compressor clutch connector. Measure resistance between terminal No. 87 (Dark Green wire) in A/C relay cavity to terminal "A" (Dark Green wire) of A/C compressor clutch connector. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, go to step 16).
  9. Measure resistance between A/C compressor clutch connector terminal "B" (Black wire) and ground. If resistance is less than 5 ohms, PCM circuits are okay. See «A/C-HEATER SYSTEM - AUTOMATIC»(/buick/riviera/viii-1994-1999/remont/automatic-hvac-system/#hvac-system-automatic) article. If resistance is greater than 5 ohms, go to step 25).
  10. Turn ignition off. Connect scan tester. Turn ignition on. Observe A/C relay control circuit in ENGINE 3 DATA VALUES. If scan tester displays ON, go to next step. If scan tester does not display ON, go to step 17).
  11. Disconnect PCM connector C1. Check for poor terminal contact at connector C1, terminal No. 27 (Dark Green/White wire). If a repair was made, go to step 18). If a repair was not made, go to step 24).
  12. Remove A/C relay. Measure voltage between A/C relay terminal No. 86 (Dark Green/White wire) and ground. If voltage is greater than .3 volt, go to step 17). If voltage is not greater than .3 volt, go to step 13).
  13. Disconnect PCM connector C1. Measure resistance between terminal No. 86 (Dark Green/White wire) in A/C relay cavity to PCM connector C1, terminal No. 27 (Dark Green/White wire). If resistance is less than5 ohms, go to next step. If resistance is greater than 5 ohms, go to step 19).
  14. If test light comes on at either terminal, go to step 20). If test light does not come on, go to step 21).
  15. Check terminal contact at A/C relay. If a terminal contact problem is found, go to step 18). If a terminal contact problem is not found, go to step 22).
  16. Check terminal contact at A/C compressor clutch connector. If a terminal contact problem is found, go to step 18). If a terminal contact problem is not found, go to step 23).
  17. Repair short to voltage in Dark Green/White wire.
  18. Repair terminal contact.
  19. Repair open in Dark Green/White wire.
  20. Repair Pink wire between splice and terminal where test light did not light.
  21. Check for an open in Pink wire between fuse and splice, short in Dark Green wire (blown fuse), shorted relay (blown fuse), or short in Pink wire (blown fuse).
  22. Replace A/C relay.
  23. Repair open in Dark Green wire.
  24. Replace PCM.
  25. Repair open in Black Ground wire.