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Discussion Starter #1 (Edited)
Air conditioner not working

We have an 08 G6 coupe with the 3.5 liter engine. A few weeks ago, the AC worked fine when the wife went to work in the morning, then nothing on the way home. I looked it over, checked fuses and relays that seemed to have anything to do with the AC and all were fine. When turning on the AC, the engine cooling fan immediately started running like it should, but the compressor was not running at all. When the refrigerant is low, I've always seen the compressors click on and off as they're trying to work, but they shut down due to low refrigerant. That was not the case here...like I said, no action from the compressor at all. Finally, I unhooked the battery for a few minutes and after hooking it back up, the AC worked flawlessly for a couple of weeks. Now, yesterday, it's doing the same thing again. ANyone have an idea of the most likely problem? I don't believe it's low refrigerant or any other major component failure, probably a faulty switch or sensor or something. There is no check engine light or anything. I assume there probably is a code that could be read even though the check engine light is not on. Thanks for any feedback. The AC system has not been touched by anyone since the car was new.

Update: After writing this question, I went out to the garage and checked the car now that it's been sitting for 17 hours and the AC is working perfectly. This problem seems to come up when the car is hot and it's been sitting out in the very hot sun for a few hours. Not nice to get in a hot car on a 95 degree day and have no AC. Obviously it's some little thing causing this problem, but figuring it out may be tough!
 

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Discussion Starter #3 (Edited)
Manual control
No abnormalities with the engine coolant gauge. No abnormalities at all except the compressor doesn't want to engage when the car is hot and has been sitting in the hot sunny weather. When the AC works, it appears to be working perfectly.
 

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Lots of possibilities. I'm out the door till tomorrow so I'll leave you with this which may or may not help:


Service Information
2008 Pontiac G6 | G6 (VIN Z) Service Manual | Document ID: 1892468
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Air Conditioning Compressor Malfunction
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description
When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CLUTCH relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

Diagnostic Aids
The following conditions must be met in order for the ECM to turn on the compressor clutch:

• The battery voltage is between 9-18 volts.

• The engine coolant temperature (ECT) is less than 123°C (253°F).

• The engine speed is less than 4,760 RPM.

• The engine speed is more than 600 RPM.

• The A/C high side pressure is between 2929-269 kPa (425-39 psi).

• The throttle position is less than 100 percent.

• The evaporator temperature is greater than 0°C (32°F).

• The ECM does not detect excessive torque load.

• The ECM does not detect insufficient idle quality.

Reference Information
Schematic Reference
HVAC Schematics

Connector End View Reference
Component Connector End Views

Description and Operation
Air Temperature Description and Operation

Electrical Information Reference

• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference
Control Module References for scan tool information

Circuit/System Testing
Ignition OFF, disconnect the A/C CLUTCH relay.
Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
⇒ If the test lamp illuminates, test the control circuit for a short to voltage.

Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
⇒ If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance.

Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
⇒ If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance.

Disconnect the harness connector at the A/C clutch coil.
Test for less than 1 ohm between the ground circuit terminal A and ground.
⇒ If greater than the specified range, test the ground circuit for an open/high resistance.

Connect the harness connector at the A/C clutch coil.
Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated.
⇒ If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.

Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
Command the A/C relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
⇒ If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒ If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.

If all circuits test normal, test or replace the A/C clutch relay.
Component Testing
Ignition OFF, disconnect the A/C COMP relay.
Test for 60-180 ohms between terminals 85 and 86.
⇒ If the resistance is not within the specified range, replace the relay.

Test for infinite resistance between the following terminals:
• 30 and 86

• 30 and 87

• 30 and 85

• 85 and 87

⇒ If not the specified value, replace the relay.

Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.
⇒ If greater than the specified range, replace the relay.

Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Relay Replacement

• Compressor Clutch Assembly Replacement

• Control Module References for ECM replacement, setup, and programming
© 2012 General Motors Corporation. All rights reserved.
 

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Discussion Starter #5
Thanks for the information. Should keep a person busy for a while running through the checklist.
 
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