Air Conditioning Compressor Malfunction. Pontiac Grand Prix 2008

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2008 🢒 Grand Prix 🢒 HVAC 🢒 HVAC - Automatic 🢒 Air Conditioning Compressor Malfunction

Air Conditioning Compressor Malfunction RPO L26/L32

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.

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
A/C Relay Coil B+	2	2	--	--
A/C Relay Switch B+	2	2	--	--
A/C Relay Control	P0645, P0646	P0645, P0647	P0645, P0647	--
A/C Clutch Control	2	2	1	--
A/C Compressor Clutch Ground	--	2	2	--
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative

When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the powertrain control module (PCM) to ground the A/C compressor clutch relay control circuit, which will switch the A/C COMP 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 PCM to turn on the compressor clutch:

•	Battery voltage is between 9-18 volts.

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

•	Engine speed is less than 4,760 RPM.

•	Engine speed is more than 600 RPM.

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

•	Throttle position is less than 100 percent.

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

•	PCM does not detect excessive torque load.

•	PCM 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

•	Air Delivery 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 Verification

Ignition ON, engine running.
Press the A/C request switch. The A/C compressor clutch should engage.
Place the mode switch in the defrost position. The A/C compressor clutch should engage.

Circuit/System Testing

Ignition OFF, disconnect the A/C COMP relay.
Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal G8 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 E8 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the A/C COMP relay.

Verify that a test lamp illuminates between the B+ circuit terminal E7 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal for a short to ground.

Disconnect the harness connector at the A/C compressor clutch.
Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal B 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 compressor clutch.
Connect a 10A fused jumper wire between the B+ circuit terminal E7 and the control circuit terminal G8. Verify the A/C compressor clutch is activated.

⇒	If the A/C compressor clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C compressor clutch.

Connect a test lamp between the ignition circuit terminal E8 and the control circuit terminal G7.
Command the A/C relay 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 PCM.

⇒	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 PCM.

If all circuits test normal, test or replace the A/C COMP relay.

Component Testing

Relay Test

Ignition OFF, disconnect the A/C COMP relay.
Test for 60-180 ohms of resistance 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 of resistance 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.

•	Control Module References for PCM setup, replacement, and programming

•	Compressor Clutch Assembly Replacement

Air Conditioning Compressor Malfunction RPO LS4