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 Switch B+ | 2 | 2 | -- | -- |
A/C Relay Coil Ignition | 2 | 2 | -- | -- |
A/C Request Signal | 2 | 2 | 2 | -- |
A/C Relay Control | P1545 | P1545 | P1545 | -- |
A/C Clutch Control | 2 | 2 | 1 | -- |
Evaporator Temperature Sensor Ground | -- | 2 | -- | -- |
A/C Compressor Clutch Ground | -- | 2 | -- | -- |
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative | ||||
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 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:
| • | 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) |
| • | ECM does not detect excessive torque load |
| • | ECM does not detect insufficient idle quality |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, command the A/C relay ON and OFF with a scan tool. Observe the HVAC compressor operation, the A/C compressor clutch should engage and disengage when changing between the commanded states.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the evaporator temperature sensor.
- Test for less than 5 ohms between the ground circuit terminal 3 and ground.
- Ignition ON, test for greater than 76 volts between the signal circuit terminal 1 and ground.
- Ignition OFF, connect the harness connector at the evaporator temperature sensor.
- Engine running, observe the scan tool BCM A/C Request parameter while cycling the A/C switch on the HVAC control module. The parameter should change between Yes and No.
- Ignition OFF, disconnect the A/C relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Disconnect the harness connector at the A/C compressor clutch.
- Test for less than 1.0 ohm between the ground circuit terminal B and ground
- Connect the harness connector at the A/C compressor clutch.
- 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.
- Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
- 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 all circuits test normal, test or replace the A/C relay.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If the parameter does not change between the specified values, test the signal circuit terminal A43 for a short to ground or an open high/resistance. If the circuit tests normal, test or replace the evaporator temperature sensor. If the A/C compressor remains inoperative, replace the BCM. |
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | 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 relay. |
| ⇒ | 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. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
