• | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Relay Switch B+ | 1 | 1 | -- | -- |
Relay Coil Ignition Voltage | 1 | 1 | -- | -- |
A/C Compressor Clutch Relay Control | P0645 | P0645 | P0645 | -- |
Relay Coil Ground | -- | 1 | -- | -- |
Compressor Clutch Ground | -- | 1 | -- | -- |
1. A/C Compressor Malfunction |
When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the engine control module (ECM) to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR CLUTCH relay on. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.
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 greater than 600 RPM |
• | Engine speed is less than 4,760 RPM |
• | A/C high side pressure is between 2929-269 kPa (39-425 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 |
• | The ambient temperature is above 1°C (34°F) |
Control Module References for scan tool information
⇒ | If the clutch does not engage refer to Air Conditioning (A/C) System Performance Test |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the A/C clutch fuse is open, test the relay switch control circuit for a short to ground. If all circuits test normal, test or replace the A/C compressor clutch. |
⇒ | 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. |
⇒ | If the test lamp remains ON all the time, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If the test lamp remains OFF all the time, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for HVAC control module and ECM replacement, setup, and programming |