A/C Signal: Description and Operation

DESCRIPTION
This signal tells the Powertrain Control Module (PCM) when the A/C mode is selected at the A/C control switch. The PCM uses this signal to adjust the idle speed before turning "ON" the A/C clutch. The A/C compressor will be inoperative if this signal is not available to the PCM.

OPERATION
A 12-volt signal is supplied to the A/C request input of the Powertrain Control Module (PCM) when the A/C is selected through the A/C control switch.

The A/C compressor clutch relay is controlled through the PCM. This allows the PCM to modify the idle air control position prior to the A/C clutch engagement for better idle quality. If the engine operating conditions are within their specified calibrated acceptable ranges, the PCM will enable the A/C compressor relay. This is done by providing a ground path for the A/C relay coil within the PCM. When the A/C compressor relay is enabled, 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. The PCM will not enable the A/C compressor clutch if any of the following conditions are met:
- The engine speed is greater than 6315 RPM.
- The Engine Coolant Temperature (ECT) is greater than 119°C (246°F).
- The throttle is more than 80% open.

PURPOSE
The A/C compressor operation is controlled by the powertrain control module (PCM) for the following reasons:
- It improves idle quality during compressor clutch engagement.
- It improves wide open throttle (WOT) performance.
- It provides A/C compressor protection from operation with incorrect refrigerant pressures.

The A/C electrical system consists of the following components:
- The A/C control switch.
- The A/C refrigerant pressure switches.
- The A/C compressor clutch.
- The A/C compressor clutch relay.
- The PCM.

A/C REQUEST SIGNAL
This signal tells the PCM when the A/C mode is selected at the A/C control switch. The PCM uses this input to adjust the idle speed before turning on the A/C clutch. The A/C compressor will be inoperative if this signal is not available to the PCM.