Circuit Description
When an A/C mode is selected, the HVAC control head supplies a battery positive voltage signal to the PCM A/C request input. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C compressor relay is engaged battery positive voltage is supplied to the compressor clutch coil. The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested unless one or more of the following conditions are present:
| • | Throttle angle is more than 90 percent. |
| • | A/C head pressure is more than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
| • | Ignition voltage is below 10.5 volts. |
| • | Engine speed is more than 5440 RPM. |
| • | ECT is more than 125°C (257°F). |
| • | IAT is less than 5°C (41°F). |
Any of the conditions described above will inhibit A/C compressor relay operation.
Diagnostic Aids
Inspect for the following:
Inspect for conditions that will disable A/C operation:
| • | Throttle angle more than 90 percent. |
| • | A/C head pressure more than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
| • | Ignition voltage less than 10.5 volts. |
| • | Engine speed more than 5440 RPM. |
| • | ECT more than 125°C (257°F). |
| • | IAT less than 5°C (41°F). |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Are any PCM DTCs stored? | -- | Diagnose DTCs first. Go to Diagnostic Trouble Code (DTC) List/Type | Go to Diagnostic System Check in HVAC |
