• | 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 |
---|---|---|---|---|
A/C CLUTCH Relay Coil Ignition | 2 | 2 | -- | -- |
A/C CLUTCH Relay Switch B+ | 2 | 2 | -- | -- |
A/C CLUTCH Relay Control | P0645 | P0645 | P0645 | -- |
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 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 CLTCH relay. 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 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 |
Control Module References for scan tool information
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.
⇒ | 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. |
⇒ | If the resistance is not within the specified range, replace the relay. |
• | 30 and 86 |
• | 30 and 87 |
• | 30 and 85 |
• | 85 and 87 |
⇒ | If not the specified value, replace the relay. |
⇒ | If greater than the specified range, replace the relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming |