For 1990-2009 cars

The A/C electrical system consists of the following components:

#### A/C System Components

• | A/C Controller

• | A/C Refrigerant Pressure Sensor

• | A/C Compressor Clutch

• | A/C Compressor Clutch Relay

• | 12 volt A/C request signal (C60, C34)

• | PCM

### A/C Request Signal

This signal is transmitted through a 12 volt signal from the Front(C60) HVAC Controller to the PCM, the 12.0 volt signal indicates that an A/C mode is selected. The PCM uses this information to adjust the idle speed before turning on the A/C clutch. If this signal is not available to the PCM, the A/C Compressor will be inoperative. Refer to Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis for A/C clutch wiring diagrams and diagnosis of A/C clutch electrical system. When diagnosing the refrigerant portion of the HVAC system, the Cooling Insufficient - Air Conditioning (A/C) System diagnosis in Heating, Ventilation and Air Conditioning should be used.

### A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor signal indicates high side refrigerant pressure to the PCM. The PCM uses this information to adjust the idle air control valve to compensate for the higher engine loads present with high A/C refrigerant pressures and to control the cooling fans. A fault in the A/C refrigerant pressure sensor signal will cause DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit to set.

When A/C is selected through the HVAC controller the PCM increases the engine idle speed just prior to A/C clutch engagement for better idle quality. In addition the PCM will command the cooling fans on during A/C operation. The PCM monitors the A/C refrigerant pressure. If the A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable ranges the PCM will enable the A/C compressor relay. This is accomplished 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 from the front A/C Control Assembly, unless any of the following conditions are met:

• | Throttle more than 90 percent

• | A/C head pressure more than 427 psi (4.27 volts) or less than 41 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

• | Ignition voltage below 9.5 volts.

• | Engine speed more than 6900 RPM for 5 seconds.

• | ECT more than 121°C (250°F).

• | IAT less than 0°C (32°F)

For more information regarding the A/C System, refer to HVAC Compressor Controls Circuit Description in HVAC Systems - Manual.