GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Refer to Engine Controls Schematic

Cell 20: A/C Compressor Controls


Object Number: 352474 Size: FS
Cell 10: IGN MAIN 2 MaxiFuse 60 A
Cell 11: DIC/HVAC and HVAC CTRL Fuses
Handling Electrostatic Discharge Sensitive Parts Notice
Cell 20: Automatic Transaxle Solenoids, and TCC Switch
Cell 20: Cooling Fan Controls
OBDII Symbol Description Notice
Cell 14: Engine Ground G117
Handling Electrostatic Discharge Sensitive Parts Notice
Cell 14: Engine Ground G117
Cell 10: Underhood Accessory Wiring Junction Block

Circuit Description

When an A/C mode is selected, the A/C control head or the A/C programmer supplies a 12 volt signal to the PCM A/C request input. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C relay is engaged, battery 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 one or more of the following conditions are present:

    • Throttle angle is greater than 96%.
    • A/C head pressure is greater than 440 psi (4.6 volts) or less than 32 psi (0.3 volt) (as determined by the A/C refrigerant pressure sensor).
    • Ignition 1 voltage is below 10 volts.
    • Engine speed is greater than 4392 RPM for less than 1 second.
    • Engine speed is greater then 4400 RPM for any amount of time.
    • ECT is greater than 124°C (255°F).
    • IAT is less than 5°C (41°F).

Any of the conditions described above will inhibit A/C compressor relay operation.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness. Inspect the wiring harness for damage.
    • If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a voltmeter connected to the A/C relay control circuit at the PCM harness connector while moving connectors and wiring harnesses related to the A/C relay. A change in voltage will indicate the location of the malfunction.

Check for conditions that will disable A/C operation:

    • Throttle angle is greater than 96%.
    • A/C head pressure is greater than 440 psi (4.6 volts) or less than 32 psi (0.3 volt) (as determined by the A/C refrigerant pressure sensor).
    • Ignition 1 voltage is below 10 volts.
    • Engine speed is greater than 4392 RPM for less than 1 seconds.
    • Engine speed is greater then 4400 RPM for any amount of time.
    • ECT is greater than 124°C (255°F).
    • IAT is less than 5°C (41°F).

Test Description

Number(s) below refer to circled number(s) on the diagnostic chart:

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 if the conditions listed under the Important are met.

    3.

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

    4.

  4. Checks the fuse to determine if the ignition feed circuit(s) are open or shorted to ground.

  5. The A/C diode (clamping diode) is used to control voltage surges that occur when the A/C clutch coil is cycled from ON to OFF. If the diode is open, the voltage surge may blow the A/C fuse.

    6.

  6. Determines whether the A/C relay current draw is the reason for the blown A/C fuse.

A/C Clutch Control Circuit Diagnosis

Step

Action

Value(s)

Yes

No

1

Was the On-Board Diagnostic (OBD) system check performed?

--

Go to Step 2

Go to 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 32°C (0.3 volts).
   • Coolant temperature must be below 121°C (250°F).

  1. A/C selector switch OFF.
  2. Ignition ON, engine OFF.
  3. Listen for engagement of the A/C clutch.

Is the A/C Clutch engage?

--

Go to Step 24

Go to Step 4

4
  1. Start the engine.
  2. Select the A/C 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 the A/C mode selected, monitor the A/C Request display on the scan tool.

Does A/C Request display Yes?

--

Go to Step 9

Go to Step 6

6

  1. Turn the ignition switch OFF and disconnect the PCM.
  2. Turn the ignition switch ON.
  3. With the A/C mode selected, measure the voltage on the A/C request circuit at the PCM connector.

Is the voltage near the specified value?

B+

Go to Step 8

Go to Step 7

7
  1. Check for the following conditions:
    2. • An open or short to ground in the A/C Request circuit
    • Poor connection(s) at the A/C control head or A/C Controller.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 42

Go to Diagnostic System Check in HVAC

8
  1. Check the A/C request circuit for a poor connection at the PCM.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 42

Go to Step 40

9

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

Is indicated A/C pressure between the specified values?

32 psi - 440 psi (0.3V-4.6V)

Go to Step 12

Go to Step 10

10
  1. Connect J 39183-C R-134a Manifold gauge set (refer to Heater, Ventilation and Air Conditioning).
  2. Observe high side refrigerant pressure on the gauge.

Is high side refrigerant pressure within the specified values?

32 psi - 440 psi (0.3V-4.6V)

Go to Step 11

Go to Refrigerant Recovery and Recharging in HVAC

11
  1. Turn the ignition switch OFF.
  2. Disconnect A/C Pressure sensor.
  3. Turn the ignition switch ON.
  4. View A/C pressure sensor display on the scan tool.

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

0 psi

Go to Step 41

Go to Step 40

12

Check the A/C Clutch Fuse

Is the fuse blown?

--

Go to Step 13

Go to Step 17

13
  1. Turn the ignition switch OFF.
  2. Remove the A/C fuse.
  3. Remove the A/C relay.
  4. Connect the test lamp to battery positive.
  5. Probe the ignition positive feeds in the A/C relay connector.

Is the test lamp ON?

--

Go to Step 31

Go to Step 14

14
  1. Leave the A/C relay disconnected.
  2. Disconnect the A/C compressor clutch coil connector.
  3. Connect the test lamp to battery positive.
  4. Probe the A/C compressor clutch feed circuit (CKT 59) in the relay connector.

Is the test lamp ON?

--

Go to Step 32

Go to Step 15

15

  1. Check for an open diode.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 42

Go to Step 16

16

  1. Turn the ignition switch OFF.
  2. Reconnect the A/C relay.
  3. Disconnect the PCM.
  4. Set the DMM to measure the 10 amp scale.
  5. Turn the ignition switch ON.
  6. Measure the current draw with the DMM connected between the A/C control circuit and ground (Monitor the reading for at least 2 minutes).

Does the DMM display a current draw within the specified values?

0.5-1.5 amps

Go to Step 38

Go to Step 39

17
  1. Turn the ignition switch OFF.
  2. Remove the A/C relay.
  3. Turn the ignition switch ON.
  4. Connect the test lamp to ground.
  5. Probe the ignition positive feed circuits to the A/C relay.

Is the test lamp ON?

--

Go to Step 18

Go to Step 33

18
  1. Leave the A/C relay disconnected.
  2. Connect a 10 amp fused jumper between an ignition positive feed and A/C compressor clutch coil circuits.

Is the A/C compressor clutch engaged?

--

Go to Step 21

Go to Step 19

19
  1. Leave the 10 amp fused jumper connected.
  2. Disconnect the A/C compressor clutch coil connector.
  3. Connect the test lamp to ground.
  4. Probe cavity B in the A/C compressor clutch coil connector.

Is the test lamp ON?

--

Go to Step 20

Go to Step 34

20
  1. Connect the test lamp to battery positive.
  2. Probe cavity A in the A/C compressor clutch coil connector.

Is the test lamp ON?

--

Go to Step 38

Go to Step 35

21
  1. Leave the A/C relay disconnected.
  2. Connect the test lamp between the ignition positive feed and A/C relay control circuit (CKT 459) in the relay connector.
  3. Using the scan tool, output functions, cycle the A/C relay ON and OFF.

Does the test lamp flash ON and OFF?

--

Go to Step 22

Go to Step 23

22
  1. Check for poor terminal connections in the A/C relay connector.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 42

Go to Step 39

23
  1. Check for the following circuit condition(s):
  2. An open in the A/C control circuit (CKT 459).
  3. Poor terminal connections at the PCM.
  4. If a problem is found repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 42

Go to Step 40

24
  1. Turn the ignition switch ON.
  2. Turn the A/C selector switch OFF
  3. Observe the A/C Request display on the scan tool.

Does the A/C Request display Yes?

--

Go to Step 25

Go to Step 27

25
  1. Turn the ignition switch OFF.
  2. Disconnect the PCM.
  3. Turn the ignition switch ON and the A/C selector OFF.
  4. Using a 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 26

Go to step 27

26
  1. Turn the ignition switch OFF and disconnect the A/C control head.
  2. Turn the ignition switch ON and check the A/C Request circuit for a short to battery positive.
  3. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 42

Go to Diagnostic System Check in HVAC

27
  1. Leave the A/C selector OFF.
  2. Disconnect the A/C relay.
  3. Start vehicle and observe the A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Step 28

Go to Step 29

28
  1. Turn the ignition switch OFF.
  2. Disconnect the A/C compressor clutch coil connector.
  3. Start the engine
  4. Observe the A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Step 38

Go to Step 36

29
  1. Turn the ignition switch OFF.
  2. Leave the A/C relay disconnected.
  3. Leave the A/C selector OFF.
  4. Connect the test lamp to battery positive.
  5. Turn the ignition switch ON, engine OFF.
  6. Probe the A/C relay control circuit (CKT 459).

Is the test lamp ON?

--

Go to Step 30

Go to Step 39

30
  1. Leave the test lamp connected to battery positive.
  2. Disconnect the PCM.
  3. Turn the ignition switch ON.
  4. Probe the A/C relay control circuit (CKT 459).

Is the test lamp ON?

--

Go to Step 37

Go to Step 40

31

Locate and repair the short to ground in the ignition positive feed circuit(s). Refer to Wiring Repairs .

Is action complete?

--

Go to Step 42

--

32
  1. Locate and repair the following circuit condition(s):
    2. •  A short to ground in the A/C compressor clutch coil feed circuit (CKT 459).
    • A shorted diode
  2. Refer to Wiring Repairs .

Is action complete?

--

Go to Step 42

--

33

Locate and repair the open ignitiion positive feed circuit(s). Refer to Wiring Repairs .

Is action complete?

--

Go to Step 42

--

34

Locate and repair the open A/C compressor clutch coil feed circuit (CKT 59). Refer to Wiring Repairs in Wiring Systems.

Is action complete?

--

Go to Step 42

--

35

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

Is action complete?

--

Go to Step 42

--

36

Locate and repair the short to voltage in the A/C compressor clutch coil feed circuit (CKT 59). Refer to Wiring Repairs in Wiring Systems.

Is action complete?

--

Go to Step 42

--

37

Locate and repair the short to ground in the A/C relay control circuit (CKT 459). Refer to Wiring Repairs .

Is action complete?

--

Go to Step 42

--

38

Replace the A/C compressor clutch coil. Refer to Heating, Ventilation and Air Conditioning.

Is action complete?

--

Go to Step 42

--

39

Replace the A/C Relay.

Is action complete?

--

Go to Step 42

--

40

Important: Replacement PCM must be programmed.

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

--

Go to Step 42

--

41

Replace A/C refrigerant pressure sensor.

Is Action complete?

--

Go to Step 42

--

42

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 32°C (0.3 volts).
   • Coolant temperature must be below 121°C (250°F).

  1. Ignition ON, 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