HVAC System - Compressor Clutch Controls: Overview GMC Sonoma II

MODEL IDENTIFICATION

Note. Metro, Prizm and Tracker, and Saturn are not covered in this article. For A/C compressor clutch diagnosis on Metro, Prizm, Tracker, and Saturn, see appropriate MANUAL A/C-HEATER SYSTEMS article.

MODEL IDENTIFICATION (CARS)

MODEL IDENTIFICATION (LIGHT TRUCKS & VANS)

Description

Powertrain Control Module (PCM) receives an A/C request signal from Instrument Panel Cluster (IPC) over UART serial data line. When A/C is requested, the 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 seconds. This allows PCM to adjust engine idle RPM for additional load.

PCM will temporarily de-energize A/C clutch relay when one or more of the following conditions occur

1. A hot engine restart.
2. Wide open throttle (TPS position over 90 percent).
3. If engine RPM is greater than 6000 RPM.
4. During Idle Air Control (IAC) valve reset

A/C clutch relay will remain de-energized when one or both of the following conditions occur

1. DTC P0530 or U1016 are set.
2. When there is no A/C request signal to PCM.

For additional trouble shooting information, go to MANUAL A/C-HEATER SYSTEMS - CAVALIER & SUNFIRE article.

Powertrain Control Module (PCM) receives an A/C request signal from Body Control Module (BCM) 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. The PCM delays grounding relay circuit for .3 seconds. This allows PCM to adjust engine idle RPM for additional load.

The PCM will temporarily de-energize A/C clutch relay when one or more of the following conditions occur

1. A hot engine restart.
2. Wide open throttle (TPS position over 90 percent).
3. If engine RPM is greater than 6000 RPM.
4. During Idle Air Control (IAC) valve reset.

A/C clutch relay will remain de-energized when one or both of the following conditions occur

1. DTC P0530 or U1016 are set.
2. When there is no A/C request signal to PCM.

For additional trouble shooting information, go to appropriate MANUAL A/C-HEATER SYSTEMS article.

Description (A/C Request Circuit)

For proper A/C system operation, the A/C request circuit monitors selected A/C mode, A/C system pressure and throttle position. When A/C mode is selected with A/C system pressure and throttle angle at a predetermined value, Engine Control Module (ECM) energizes A/C clutch relay through A/C clutch relay control circuit. The ECM de-energizes A/C clutch relay during wide open throttle, when engine coolant temperature or A/C system pressure exceeds a predetermined threshold, or when a non-A/C mode is selected. If system does not operate as specified, see A/C REQUEST CIRCUIT DIAGNOSIS .

Description (A/C Load Signal Circuit)

The ECM receives a signal from the A/C load signal circuit. A normally open pressure switch connected to battery voltage monitors A/C system operating pressures. If pressures reach approximately 175 psi (12.2 kg/cm 2 ) the switch will close, sending a signal to the ECM. The ECM will raise idle speed around 50 RPM to compensate for the additional load. If system does not operate as specified, see A/C LOAD SIGNAL CIRCUIT DIAGNOSIS .

Description (A/C Compressor Control Circuit)

The ECM controls the ground side of the A/C clutch relay to energize the A/C compressor clutch. When component is commanded on by the ECM, voltage on the control circuit should be at or near zero volts. When component is commanded off by the ECM, voltage on the control circuit should be at or near battery voltage. If system does not operate as specified, see A/C COMPRESSOR CONTROL CIRCUIT DIAGNOSIS .

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, the 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.

The PCM will enable A/C 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 ) with A/C refrigerant pressure sensor reading greater than 4.27 volts.
3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ) with A/C refrigerant pressure sensor reading greater than .40 volts.
4. Ignition voltage is less than 10.5 volts.
5. Engine speed is greater than 4500 RPM for 5 seconds or at 5400 RPM for any amount of time.
6. Engine coolant temperature is greater than 257°F (125°C).
7. Intake air temperature is less than 41°F (5°C).

Powertrain Control Module (PCM) receives an A/C request signal from Body Control Module (BCM) 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. The PCM delays grounding relay circuit for .3 seconds. This allows PCM to adjust engine idle RPM for additional load.

The PCM will disengage A/C compressor clutch if one or more of the following conditions occur

1. Throttle angle is greater than 90 percent.
2. A/C head pressure is greater than 440 psi (31 kg/cm 2 ) with A/C refrigerant pressure sensor reading greater than 4.27 volts.
3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ) with A/C refrigerant pressure sensor reading greater than .40 volts.
4. Ignition voltage is less than 10.5 volts.
5. Engine speed is greater than 4300 RPM for 5 seconds or at 5400 RPM for any amount of time.
6. Engine coolant temperature is greater than 255°F (124°C).
7. Intake air temperature is less than 41°F (5°C).

Description (A/C Request Circuit - Manual HVAC System)

When A/C is requested from the Heating, Ventilation and Air Conditioning (HVAC) control head, the A/C system sends a 12 volt signal from the HVAC control head to the PCM. The PCM then grounds the A/C relay circuit to energize the relay to allow current to flow to the A/C compressor clutch. The PCM will de-energize the A/C relay if one or more of the following conditions occur

1. High coolant temperature.
2. Low A/C system pressures.
3. High A/C system pressures.
4. Wide Open Throttle (WOT) operation.
5. High engine RPM.
6. Specific DTCs are set in the PCM.

When A/C request is detected by the PCM, the cooling fans will be turned on after A/C pressures are high enough. For diagnosis and repair, see A/C REQUEST CIRCUIT DIAGNOSIS (MANUAL HVAC) .

Description (A/C Request Circuit - Automatic HVAC)

When A/C is requested from the Heating, Ventilation and Air Conditioning (HVAC) control head, the A/C system sends a Class 2 serial data message from the HVAC control head to the PCM. The PCM then grounds the A/C relay circuit to energize the relay to allow current to flow to the A/C compressor clutch. The PCM will de-energize the A/C relay if one or more of the following conditions occur

1. High coolant temperature.
2. Low A/C system pressures.
3. High A/C system pressures.
4. Wide Open Throttle (WOT) operation.
5. High engine RPM.
6. Specific DTCs are set in the PCM.

When A/C request is detected by the PCM, the cooling fans will be turned on after A/C pressures are high enough. For diagnosis and repair, see A/C REQUEST CIRCUIT DIAGNOSIS (AUTOMATIC HVAC) .

When A/C mode is selected, a 12-volt signal is supplied to the 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 done by providing a ground path for A/C clutch relay coil through PCM. When A/C clutch relay is enabled, battery voltage is supplied to compressor clutch coil.

The 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 ) with A/C refrigerant pressure sensor reading greater than 4.27 volts.
3. A/C head pressure is less than 34 psi (2.5 kg/cm 2 ) with A/C refrigerant pressure sensor less than 0.35 volts.
4. Ignition voltage is less than 10 volts.
5. Engine speed is greater than 4225 RPM for longer than 5 seconds.
6. Engine speed is greater than 5280 RPM for any amount of time.
7. Engine coolant temperature is greater than 257°F (125°C).
8. Intake air temperature is less than 32°F (0°C).

When A/C mode is selected, a 12-volt signal is supplied to the A/C request input terminal of PCM. The 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 an acceptable range, PCM will enable A/C clutch relay. This is done by providing a ground path for A/C clutch relay coil through PCM. When A/C clutch relay is enabled, battery voltage is supplied to compressor clutch coil.

The 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 34 psi (2.5 kg/cm 2 ).
4. Ignition voltage is less than 10.5 volts.
5. Engine speed is greater than 5440 RPM.
6. Engine coolant temperature is greater than 257°F (125°C).
7. Intake air temperature is less than 41°F (5°C).

When A/C mode is selected, a 12-volt signal is supplied to the A/C request input terminal of PCM. The 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 an acceptable range, the PCM will enable A/C clutch relay by providing a ground path for the A/C clutch relay. When A/C clutch relay is enabled, battery voltage is supplied to A/C compressor clutch coil.

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

1. Throttle angle is greater than 96 percent.
2. A/C head pressure is greater than 440 psi (30.9 kg/cm 2 ).
3. A/C head pressure is less than 32 psi (2.2 kg/cm 2 ).
4. Ignition voltage is less than 10 volts.
5. Engine speed is greater than 4392 RPM for one second on Grand Prix; or greater than 4400 RPM for any length of time on Grand Prix, Lumina and Monte Carlo.
6. Engine coolant temperature is greater than 255°F (124°C).
7. Intake air temperature is less than 41°F (5°C).

When A/C mode is selected, a 12-volt signal is supplied to the A/C request input terminal of PCM. The A/C clutch relay is controlled through Powertrain Control Module (PCM), which also monitors A/C refrigerant pressure. If A/C refrigerant pressure and engine operating conditions are within an acceptable range, the PCM will enable A/C clutch relay by providing a ground path for A/C clutch relay. When A/C clutch relay is enabled, battery voltage is supplied to A/C compressor clutch coil.

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

1. Throttle angle is greater than 96 percent.
2. A/C head pressure is greater than 440 psi (30.9 kg/cm 2 ).
3. A/C head pressure is less than 32-35 psi (2.3-2.5 kg/cm 2 ).
4. Ignition 1 voltage is less than 9.5 volts.
5. Engine speed is greater than 4392 RPM for more than one second on VIN K engine, or greater than 4392 RPM for any amount of time on VIN 1 engine.
6. Engine speed is greater than 4400 RPM for any amount of time.
7. Engine coolant temperature is greater than 255°F (124°C).
8. Intake air temperature is less than 41°F (5°C).

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

When A/C control head is placed in A/C mode, a request signal is sent to PCM. The PCM will then energize A/C clutch relay, unless abnormally high or low A/C pressure is detected by A/C pressure switches. The PCM also monitors A/C low temperature sensors to cycle compressor clutch on and off. If PCM detects an A/C evaporator temperature less than 36°F (2°C), PCM will not allow A/C compressor clutch to engage. The PCM will also energize cooling fans when A/C is requested.

When A/C Programmer (ACM) requests A/C operation from PCM, the PCM will ground A/C clutch relay coil. When A/C clutch relay coil is grounded, A/C compressor clutch is energized. The PCM will disable or inhibit compressor operation during high power steering load, if engine is not running, if engine is running at wide open throttle, if ambient temperature is less than 40°F (4°C), or when certain PCM DTCs are set. The A/C compressor clutch is also disengaged during engine cranking in colder weather to prevent A/C slugging.

When A/C Programmer (ACM) requests A/C operation from PCM, the PCM will ground A/C clutch relay coil. When A/C clutch relay coil is grounded, compressor clutch is energized. PCM will disable or inhibit compressor operation during high power steering load, if engine is not running, if engine is running at wide open throttle, if ambient temperature is less than 40°F (4°C) or when certain PCM DTCs are set. The compressor clutch is also disengaged during engine cranking in colder weather to prevent A/C slugging.

The A/C clutch relay is PCM controlled to delay A/C compressor clutch engagement after A/C is turned on. This allows PCM to adjust engine RPM before the A/C compressor clutch engages. The PCM will engage compressor clutch any time A/C has been requested, unless one or more of the following conditions occur

1. Coolant temperature is high.
2. A/C system pressure is low.
3. A/C system pressure is high.
4. During wide open throttle.
5. High engine RPM.
6. Certain DTCs are set.

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

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

Note. The following test applies only to A/C request circuit. If A/C request circuit is okay and no DTCs are set, but A/C compressor clutch will not engage, further diagnosis is necessary. See appropriate MANUAL A/C-HEATER SYSTEMS article.

The PCM receives an A/C request signal from A/C selector switch 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 clutch relay is energized. After A/C request has been selected, PCM will delay grounding A/C clutch relay control circuit for .3 seconds. This allows PCM to adjust engine idle RPM for additional load. The A/C clutch relay is energized unless one or more of the following conditions occur

1. Hot engine restart.
2. Engine speed is greater than 6000 RPM.
3. During wide open throttle.
4. During Idle Air Control (IAC) valve reset.

The A/C clutch relay will remain de-energized when DTC P0530 is set, or if there is no A/C request signal due to an open A/C select switch circuit. For additional diagnosis, see appropriate MANUAL or AUTOMATIC A/C-HEATER SYSTEMS article.

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

The PCM will enable A/C 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).

The A/C clutch relay is controlled by Vehicle Control Module (VCM) to delay A/C compressor clutch engagement after A/C is turned on. This allows VCM to adjust engine RPM before A/C compressor clutch engages. VCM will engage A/C compressor 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 clutch 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 VCM, cooling fans will turn on when A/C pressure is greater than a predetermined value.

The PCM controls operation of A/C clutch relay. When any A/C mode is selected on Heating, Ventilation and Air Conditioning (HVAC) control module, a 12-volt signal is sent through the A/C high pressure switch and to the PCM. If conditions are met, the PCM will send another 12-volt signal to the A/C compressor cycling switch, which is the ground signal. When these two signals are received by the PCM, the PCM supplies a ground for the A/C relay.

The PCM controlled HVAC system consists of the following components

1. A/C high pressure switch.
2. A/C compressor cycling switch.
3. A/C compressor relay.
4. PCM

The PCM will engage the A/C compressor clutch unless one or more of the following conditions occur

1. Throttle angle at 100 percent.
2. A/C compressor cycling switch pressure is less than 18 psi (1.2 km/cm 2 ) or greater than 49 psi (3.4 km/cm 2 ).
3. A/C high pressure cut-out switch pressure is greater than 420 psi (29.5 km/cm 2 ).
4. Engine speed is greater than 5500 RPM.
5. Engine coolant temperature greater than 250°F (121°C).

Any condition described above will prevent operation of the A/C compressor clutch.