Circuit Description
When an A/C mode is selected, the A/C control head or the A/C programmer supplies a 12 volt 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 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 greater than 90 percent. |
| • | A/C head pressure is greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
| • | Ignition 1 voltage is below 10.5 volts. |
| • | Engine speed is greater than 4,500 RPM for longer than 5 seconds. |
| • | Engine speed is greater then 5,400 RPM for any amount of time. |
| • | ECT is greater 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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Are any PCM DTCs stored? | -- | Diagnose DTCs first. Go to Powertrain Control Module Diagnosis | Go to Diagnostic System Check |
