Air Conditioning Compressor Malfunction RPO L18/LLY

Ignition voltage is supplied to the mode switch from the blower motor switch. The blower motor switch must be in any position except for OFF for A/C operation. The mode switch must be in one of the following positions for an A/C request:

Once the mode switch is in one of these positions, the mode switch applies ignition voltage to the A/C high pressure switch. If the A/C high pressure switch is closed, the voltage will then be applied to the powertrain control module (PCM), for the 8.1L (RPO L18), or engine control module (ECM), for the 6.6L (RPO LLY). The voltage applied to the ECM/PCM is an A/C request signal. The ECM/PCM then monitors the voltage on the A/C low pressure switch signal. If the voltage is low near ground, then the ECM/PCM will enable the A/C compressor clutch relay. The ECM/PCM provides a ground for the relay so it can close it internal contacts.

The following conditions must be met in order for the ECM/PCM to engage the A/C compressor clutch:

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool A/C Request Signal parameter while changing the mode switch from OFF to Defrost, the reading should change from No to Yes.

⇒	If the reading does not change while switching between the commanded states, refer to A/C Request Malfunction.

2. Observe the scan tool A/C Compressor Cycling Switch parameter. The reading should be normal.

⇒	If not the specified value, refer to Low Pressure Switch Malfunction.

3. Command the A/C relay ON and OFF with a scan tool. Observe the A/C compressor operation, the A/C compressor clutch should engage and disengage when changing between the commanded states.

⇒	If the A/C compressor does not engage or does not disengage, refer to A/C Compressor Malfunction.

A/C Request Malfunction

1. Ignition OFF, disconnect the harness connector at the A/C high pressure switch.
2. Ignition ON, mode set to Defrost, verify that a test lamp illuminates between the control circuit terminal B and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal refer to Blower Motor Malfunction.

3. Verify the scan tool A/C Request Signal parameter is No.

⇒	If not the specified value, test the signal circuit terminal A for a short to voltage. If the circuit tests normal, replace the ECM/PCM.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the control circuit terminal B. Verify the scan tool A/C Request Signal parameter is Yes.

⇒	If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM/PCM.

5. If all circuits test normal, test or replace the A/C high pressure switch.

Low Pressure Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the A/C low pressure switch.
2. 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.

3. Verify the scan tool A/C Compressor Cycling Switch parameter is Normal.

⇒	If not the specified value, test the signal circuit terminal B for short to ground. If the circuit tests normal, replace the ECM/PCM.

4. Install 3A fuse jumper between the signal circuit terminal B and the ground circuit terminal A. Verify the scan tool A/C Compressor Cycling Switch parameter is Low Pressure.

⇒	If not the specified value, test the signal circuit for short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM/PCM.

5. If all circuits test normal, test or replace the A/C low pressure switch.

A/C Compressor Malfunction

1. Ignition OFF, disconnect the A/C compressor clutch relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignition circuit terminal 86 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 breaker/fuse is open, test or replace the A/C compressor clutch relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Disconnect the harness connector at the A/C compressor clutch.
6. Test for less than 1.0 ohm between the A/C compressor clutch ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the A/C compressor clutch.
8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. 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, replace the A/C compressor.

9. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
10. 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 ECM/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 ECM/PCM.

11. If all circuits test normal, test or replace the A/C compressor clutch relay.

Relay Test

1. Ignition OFF, disconnect the A/C compressor clutch relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. 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.

4. 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Air Conditioning Compressor Malfunction RPO LG4/LG5

Ignition voltage is supplied to the mode switch from the blower motor switch. The blower motor switch must be in any position except for OFF for A/C operation. The mode switch must be in one of the following positions for an A/C request:

Once the mode switch is in one of these positions, the mode switch applies ignition voltage to the A/C high pressure switch. If the A/C high pressure switch is closed, the voltage will then be applied to the A/C compressor relay and the engine control module (ECM). The voltage applied to the ECM is an input, this ensures idle quality. For the relay to close its internal contacts to supply the A/C compressor clutch with battery positive voltage, the A/C low pressure must be closed to provide a path to ground for the relay coil through the A/C low pressure switch signal circuit.

The following conditions must be met to engage the A/C compressor clutch:

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool A/C Request Signal parameter while changing the mode switch from OFF to Defrost, the reading should change from No to Yes.

⇒	If the reading does not change while switching between the commanded states, refer to A/C Request Malfunction.

2. Observe the A/C compressor operation while changing the mode switch from OFF to Defrost, the A/C compressor clutch should engage and disengage when changing between the commanded states.

⇒	If the A/C compressor does not engage or does not disengage, refer to A/C Compressor Malfunction.

A/C Request Malfunction

1. Ignition OFF, disconnect the harness connector at the A/C high pressure switch.
2. Ignition ON, mode set to Defrost, verify that a test lamp illuminates between the control circuit terminal A and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal refer to Blower Motor Malfunction.

3. Verify the scan tool A/C Request Signal parameter is No.

⇒	If not the specified value, test the signal circuit terminal B for a short to voltage. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal B and the control circuit terminal A. Verify the scan tool A/C Request Signal parameter is Yes.

⇒	If not the specified value and the A/C high side pressure is within specifications, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the A/C high pressure switch.

A/C Compressor Malfunction

1. Ignition OFF, disconnect the A/C compressor clutch relay.
2. Ignition ON, mode set to Defrost, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the control circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 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 87 for a short to ground.

5. Ignition OFF, disconnect the harness connector at the A/C compressor clutch.
6. Test for less than 1.0 ohm between the ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the A/C compressor clutch.
8. Ignition ON, connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. 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, replace the A/C compressor clutch.

9. Ignition OFF, connect the A/C compressor clutch relay and disconnect the A/C low pressure switch.
10. Test for less than 1.0 ohm between the ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

11. Ignition ON, test for ignition voltage between the control circuit terminal A and ground.

⇒	If not the specified value, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the A/C compressor clutch relay.

12. If all circuits test normal test or replace the A/C low pressure switch.

Relay Test

1. Ignition OFF, disconnect the A/C compressor clutch relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. 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.

4. 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.