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

Refer to

Cell 21: Engine Data Sensors-A/C Compressor Controls


Object Number: 344666 Size: FS
Engine Controls Components
Powertrain Control Module Description
Cell 11: HVAC (4), ABS (13), and Cruise Control (22) Fuses
Cell 10: Fuses 4, 7, 11, 13, 20, 22, 29, 38, and Circuit Breaker C
Cell 10: Fuses 12, 21, 30, 33, 39, and 42
Cell 21: Engine Data Sensors-Cooling Fan Controls
Cell 21: Engine Data Sensors-Automatic Transaxle
OBD II Symbol Description Notice
Cell 14: G117
Handling ESD Sensitive Parts Notice

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 compressor 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 then 4400 RPM for any amount of time.
    • ECT is less 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 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 A On-Board Diagnostic (OBD) system check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any DTCs stored?

--

Diagnose the DTCs first.

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 Functional Check

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 a J 39183-C .
  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

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 a 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 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 in the relay connector.
  3. Using the scan tool, output functions, cycle the A/C relay ON and OFF.

Does the test lamp turn 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.
  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 HVAC Compressor Controls System Check

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.

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.

I s 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.
    • 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. Refer to Wiring Repairs .

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. Refer to Wiring Repairs .

Is action complete?

--

Go to Step 42

--

37

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

Is action complete?

--

Go to Step 42

--

38

Replace the A/C compressor clutch coil. Refer to Compressor Clutch Coil Removal (V5 - Direct Mount) or Clutch Rotor and/or Bearing Removal (V5 - Conventional Mount) .

Is action complete?

--

Go to Step 42

--

39

Replace the A/C Relay. Refer to Compressor Relay Replacement

Is action complete?

--

Go to Step 42

--

40

Important::  Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is action complete?

--

Go to Step 42

--

41

Replace A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement

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