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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L 🢒 Air Conditioning (A/C) Compressor Control Circuit Diagnosis
Table 1: A/C Compressor Control Circuit Diagnosis (CJ2)
Table 2: A/C Compressor Control Circuit (CJ3, C60)

Refer to Engine Controls Schematics

Cell 20: A/C Compressor Controls


Object Number: 349314 Size: FS
Cell 20: Coolant Fans
OBDII Symbol Description Notice
Cell 20: Automatic Transaxle and TCC Switch
Cell 10: Accessory Time Delay Relay, and Ignition Switch
Cell 10: Ignition Switch
Cell 11: LOW BLOWER, CRUISE and HVAC Fuses
Cell 11: TURN SIGNALS CORN LPS, AIR BAG, CLUSTER, DRL and PCM-BCM U/H RELAY Fuses
Cell 10: Underhood Accessory Wiring Junction Block
Cell 10: Underhood Accessory Wiring Junction Block
Cell 14: G100, G111, G113, and G117
Cell 14: G113, and G117
Cell 14: G100, G111, G113, and G117
Cell 14: G113, and G117
Handling Electrostatic Discharge Sensitive Parts Notice
 , HVAC Compressor Control Schematics in HVAC System-Manual, or HVAC Compressor Control Schematics in HVAC System-Automatic.

Circuit Description

When A/C is selected through the A/C controller a signal is supplied to the PCM through two different methods depending on the vehicle content. The first is by Class II serial data circuit (CJ2, and the second is by a 12 volt A/C request circuit to the PCM (CJ3, C60). The PCM monitors the A/C refrigerant pressure. If the A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable ranges the PCM will enable the A/C Relay. This is accomplished by providing a ground path for the A/C Relay coil within the PCM. When the A/C compressor relay is enabled battery positive voltage is supplied to the compressor clutch coil.

The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested, unless any of the following conditions are met:

    •  Throttle greater than 96%.
    •  A/C Pressure Sensor greater than 440 psi (4.6 volts) or less than 35 psi (0.35 volt) (as determined by the A/C Pressure Sensor).
    •  Ignition voltage below 10 volts.
    •  Engine speed greater than 4700 RPM.
    •  ECT greater than 125°C (257°F).
    •  IAT less than 5°C (41°F).
    •  Class II communication error between the HVAC controller and the PCM (CJ2).
    •  An open or a short to ground in the 12 Volt A/C request circuit (CJ3, C60).

Diagnostic Aids

Inspect for the following:

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

    •  Poor terminal connection.
         Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems.
    •  Damaged harness.
         Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.
    •  Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.

A/C Compressor Control Circuit Diagnosis (CJ2)

Step

Action

Values

Yes

No

1

Was the Powerrtrain OBD System Test performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any PCM or HVAC DTCs stored?

--

Diagnose the applicable DTCs

Go to Step 3

3

Important: :  The following conditions must be met before continuing with this step:

   •  Ambient air temperature must be above 5°C (41°F).
   •  A/C Pressure must be above 35 PSI (0.4 volts).
   •  Coolant temperature must be below 121°C (250°F).

  1. Turn the A/C Selector Switch to the off position.
  2. Turn the ignition switch to the on position (engine off).
  3. Test for the engagement of the A/C clutch.

Is the A/C Clutch engaged?

--

Go to Step 13

Go to Step 4

4
  1. Start and operate the engine at 1000 - 1500 RPM.
  2. Turn the A/C selector switch to an A/C mode.
  3. Observe A/C clutch.

Is the A/C clutch engaged?

--

Refer to Diagnostic Aids

Go to Step 5

5
  1. Leave the A/C selector switch turned to an A/C mode.
  2. Observe the A/C Request display on the scan tool.

Does the A/C Request display YES?

--

Go to Step 8

Go to Step 6

6

Observe the A/C pressure sensor display on the scan tool.

Does the A/C pressure sensor indicate a voltage between the specified values?

0.4V - 4.6V

Go to System Performance Test in HVAC System

Go to Step 7

7
  1. Connect a J 39500-B Refrigerant Recovery, Recycling, and Recharging (ACR4) to monitor high side refrigerant pressure.
  2. Observe high side refrigerant pressure on the J 39500-B Refrigerant Recovery, Recycling, and Recharging (ACR4) gauge.

Is high side refrigerant pressure within the specified values?

35 psi - 440 psi

Go to VDOT A/C System Diagnosis in HVAC System

Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit

8

Inspect the A/C clutch fuse.

Is the A/C cutch fuse blown?

--

Go to Step 9

Go to Step 10

9
  1. Remove the A/C clutch fuse.
  2. Remove the A/C Relay.
  3. Test for the following circuit condition(s):
    4. •  Short to ground in the battery positive feed to the A/C relay
    •  Short to ground in the battery positive feed to the A/C clutch
    •  Shorted diode
  4. If a problem is found, repair as necessary. Refer to Repair Procedures in Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 18

Go to Step 15

10
  1. Remove the A/C relay.
  2. Connect a 10A fused jumper between the battery positive and A/C clutch coil feed cavities in the A/C relay connector.

Is the A/C clutch engaged?

--

Go to Step 12

Go to Step 11

11
  1. Test for the following circuit condition(s):
    2. •  Open in the battery positive feed circuit to the A/C relay
    •  Open in the battery positive feed circuit to the A/C clutch
    •  Open in the A/C clutch ground circuit
    •  Poor terminal connections in the A/C clutch coil connector
  2. If a problem is found, repair as necessary. Refer to Repair Procedures in Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 18

Go to Step 15

12
  1. Test for poor terminal connections in the A/C Relay in

    Underhood Accessory Wiring Junction Block (RPO L82)
    Object Number: 358519 Size: LF
    .
  2. If a problem is found, repair as necessary. . Refer to Repair Procedures in Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 18

Go to Step 16

13
  1. Turn the ignition switch to the off position.
  2. Remove the A/C relay.
  3. Turn the ignition switch to the on position.

Is the A/C clutch engaged?

--

Go to Step 14

Go to Step 16

14

Disconnect the A/C clutch connector.

Is the A/C clutch engaged?

--

Go to Step 15

Go to Step 17

15

Replace the A/C clutch.

Is the action complete?

--

Go to Step 18

--

16

Replace the A/C relay. Refer to Compressor Relay Replacement in HVAC System.

Is the action complete?

--

Go to Step 18

--

17

Locate and repair the short to voltage in the battery positive feed circuit to the A/C clutch. Refer to Repair Procedures in Wiring Repairs in Wiring System.

Is th action complete?

--

Go to Step 18

--

18

Important: :  The following conditions must be met before continuing with this step:

   •  Ambient air temperature must be above 5°C (41°F).
   •  A/C pressure must be above 35 psi (0.4 volts).
   •  Coolant temperature must be below 121°C (250°F).

  1. Start and operate the engine between 1000-1500 RPM.
  2. Turn the A/C selector switch to the on position.
  3. Listen for engagement of the A/C clutch.
  4. Wait 5 seconds and then turn the A/C selector switch to the off position.
  5. Listen for disengagement of the A/C clutch.

Did the A/C clutch engaged and disengage?

--

System OK

Go to Step 3

Test Description

The numbers below refer to numbers on the Diagnostic Table:

The A/C compressor clutch should not be engaged with the engine running if an A/C mode is not selected at the control head.

  1. Stored Diagnostic Trouble Codes (That may not illuminate the Malfunction indicator Lamp) may disable the A/C compressor. This Diagnostic Table may lead to improper diagnosis and replacement of good parts if Diagnostic Trouble Codes are present.

    2.

  2. The A/C compressor clutch should apply within 3-6 seconds, if the conditions under the Notice have been met.

  3. Checks for an A/C request signal from the A/C controller to the PCM.

    4.

  4. Checks the ignition feed circuit to the A/C relay.

    5.

  5. Determines whether the A/C relay or the circuitry is at fault.

    6.

  6. Determines whether or not the PCM is turning the A/C relay on due to a false A/C request.

    7.

  7. Isolates problem to the A/C control head or the PCM.

A/C Compressor Control Circuit (CJ3, C60)

Step

Action

Value(s)

Yes

No

1

Was the Powertrain OBD System Check performed?

--

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2

Are any PCM DTCs stored?

--

Go to applicable DTCs

Go to Step 3

3

Important: :  The following conditions must be met before continuing with this step:

   •  Ambient air temperature must be above 5°C (41°F).
   •  A/C Pressure must be above 35 psi (0.4 volts).
   •  Coolant temperature must be below 121°C (250°F).

  1. Start the engine.
  2. Turn the A/C selector switch on.
  3. Listen for engagement of the A/C clutch.

Is the A/C Clutch engaged.

--

Go to Step 18

Go to Step 4

4
  1. Start the engine.
  2. Select Defrost or MAX mode on HVAC control head.
  3. Observe A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Diagnostic Aids

Go to Step 5

5

With Defrost or Max mode selected, monitor A/C Request on the scan tool.

Does A/C Request display Yes?

--

Go to Step 9

Go to Step 6

6

  1. Turn the ignition off.
  2. Disconnect the PCM.
  3. Turn the ignition on.
  4. With Defrost or Max mode selected, measure voltage on the A/C request circuit at the PCM harness connector.

Does the voltage measure near the specified value?

B+

Go to Step 8

Go to Step 7

7
  1. Test the A/C request circuit for the following conditions:
    2. •  Open
    •  Shorted to ground
    •  Poor connection at the A/C control head or A/C programmer (as applicable).
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs and Wiring Repairs .

Was a problem found?

--

Go to Step 29

Go to A Diagnostic System Check

8
  1. Test the A/C request circuit for a poor connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 29

Go to Step 27

9

Observe A/C refrigerant pressure display on the scan tool.

Is indicated A/C pressure between the specified values?

36 - 440 psi

Go to Step 12

Go to Step 10

10
  1. Connect J 39183-C R-134a Manifold gauge set.
  2. Observe high side refrigerant pressure on the J 39183-C R-134a Manifold gauge set.

Is high side refrigerant pressure within the specified values?

36 - 440 psi

Go to Step 11

Go to System Performance Test in HVAC System

11
  1. Turn the ignition off.
  2. Disconnect the A/C Pressure sensor.
  3. Turn the ignition on.
  4. View A/C Highside display on the scan tool engine data list.

Does the scan tool display an A/C Highside pressure at the specified value?

0 psi

Go to Step 28

Go to Step 27

12

  1. Disconnect the A/C relay in the

    Underhood Accessory Wiring Junction Block (RPO L82)
    Object Number: 358519 Size: LF
    .
  2. Probe the ignition feed circuits at the A/C relay cavities in the

    Underhood Accessory Wiring Junction Block (RPO L82)
    Object Number: 358519 Size: LF
    with a J 35616-200 test lamp to ground.

Is the J 35616-200 test lamp on?

--

Go to Step 13

Go to Step 23

13

Connect a fused jumper between the ignition feed circuit and A/C compressor clutch control circuit at the A/C Relay in the

Underhood Accessory Wiring Junction Block (RPO L82)


Object Number: 358519 Size: LF
.

Does the A/C compressor clutch engage?

--

Go to Step 14

Go to Step 15

14
  1. Test for poor connections at A/C relay.
  2. If a problem is found, replace faulty terminals as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 29

Go to Step 24

15
  1. Disconnect the A/C compressor clutch electrical connector (leave the ignition control circuit and A/C compressor clutch control circuit jumpered at the A/C Relay in the

    Underhood Accessory Wiring Junction Block (RPO L82)
    Object Number: 358519 Size: LF
    ).
  2. Connect a J 35616-200 test lamp between A/C compressor clutch feed circuit and the compressor ground circuit.

Is the J 35616-200 test lamp on?

--

Go to Step 16

Go to Step 17

16
  1. Test for poor connections at the A/C compressor clutch.
  2. If a problem is found, replace faulty terminals as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 29

Go to Step 25

17
  1. Test for an open or short to ground in the A/C compressor clutch control circuit.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 29

Go to Step 26

18
  1. Turn the ignition on.
  2. Turn the A/C off.
  3. Observe A/C Request display on the scan tool.

Does A/C Request display Yes?

--

Go to Step 19

Go to Step 21

19
  1. Turn the ignition off.
  2. Disconnect the PCM.
  3. Turn the ignition on, and leave the A/C off.
  4. Using a J 39200 DMM, measure voltage between the A/C request circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

B+

Go to Step 20

Go to Step 27

20
  1. Turn the ignition off.
  2. Disconnect the A/C controller.
  3. Turn the ignition on.
  4. Test the A/C Request circuit for a short to battery positive voltage.

If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 29

Go to A Diagnostic System Check

21

  1. Disconnect A/C relay.
  2. Start vehicle and observe the A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Step 22

Go to Step 24

22

Locate and repair short to voltage in the A/C compressor clutch control circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 29

--

23

Repair open or short to ground in ignition feed circuit to the A/C Relay. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 29

--

24

Replace A/C Relay.

Is the action complete?

--

Go to Step 29

--

25

Repair A/C compressor clutch.

Is the action complete?

--

Go to Step 29

--

26

Locate and repair open in A/C compressor clutch ground circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 29

--

27

Important: :  The replacement PCM must be programmed.

Replace the PCM. Refer to PCM Replacement/Programming .

Is the action complete?

--

Go to Step 29

--

28

Replace A/C refrigerant pressure sensor.

Is the action complete?

--

Go to Step 29

--

29

Important: :  The following conditions must be met before continuing with this step:

   •  Ambient air temperature must be above 5°C (41°F).
   •  A/C Pressure must be above 35 psi (0.4 volts).
   •  Coolant temperature must be below 121°C (250°F).

  1. Turn the ignition on, and leave the engine running.
  2. Turn A/C selector switch on.
  3. Listen for engagement of the A/C clutch.

Is the A/C Clutch engage.

--

System OK

Go to Step 3