Powertrain Control Module Controlled Air Conditioning Description. Oldsmobile Shelby Series 1 1999

For 1990-2009 cars

In order to improve engine operation, and protect the A/C compressor and A/C clutch during wide open throttle (WOT) performance, the A/C compressor operation is controlled by the PCM.

This A/C system consists of the following components:

• | The heater and A/C control

• | The A/C clutch relay

• | The A/C compressor clutch

• | The PCM

When the heater and A/C control is placed in the A/C mode, a request signal is sent to the PCM. The PCM then energizes the A/C clutch relay. The PCM also turns the cooling fans ON when A/C is requested. The A/C clutch relay is controlled by the PCM so that the PCM can increase idle speed before turning ON the A/C compressor clutch or disable the A/C compressor clutch during WOT, or high coolant temperature.

The PCM energizes the A/C clutch whenever the engine is running less than 3,950 RPM and A/C has been requested. The PCM will not energize the A/C clutch whenever any of the following conditions are present:

• | Throttle angle more than 86 percent

• | Ignition voltage less than 10 volts

• | Engine speed more than 4294 RPM

• | ECT more than 125°C (257°F) -- The PCM re-enables the A/C at 121°C (250°F).

The scan tool is used in diagnosing the A/C system. The PCM has the ability to display the following parameters:

• | A/C request input to the PCM

• | A/C compressor status

• | A/C clutch ON or OFF status