Powertrain Control Module Controlled Air Conditioning Description. Chevrolet Alero Export 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Alero Export 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Powertrain Control Module Controlled Air Conditioning Description

IAT, MAF, A/C Pressure Sensors, Cruise Control Module


(1)	Intake Air Temperature (IAT) Sensor
(2)	Mass Air Flow (MAF) Sensor
(3)	A/C Referigerant Pressure Sensor
(4)	Cruise Control Module

The air conditioning system uses a compressor with variable displacement.

The A/C compressor clutch is controlled by the Body Control Module (BCM). The BCM sends the A/C request to the Powertrain Control Module (PCM) via the Class II serial data circuit. This allows the PCM to manage idle quality, improve wide open throttle performance, and to protect the A/C system from excessively high and low pressures.

The PCM controlled air conditioning system uses a variable displacement compressor referred to as a V-5 compressor. The V-5 compressor meets the A/C requirements without cycling. For a description of the system and an explanation of the components used, refer to the Air Conditioning System portion of the service manual.

For a description of the system and an explanation of the components used, refer to HVAC.

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

•	A/C control head

•	A/C refrigerant pressure switch

•	A/C compressor clutch

•	A/C compressor clutch relay

•

PCM

When A/C is selected through the A/C control head a signal is communicated via Class II to the PCM. The A/C compressor clutch relay is controlled through the PCM. This allows the PCM to increase 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, unless any of the following conditions are met:

•	Throttle greater than 90%

•	A/C head pressure greater 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 greater than 6900 RPM for 5 seconds.

•	ECT greater than 121°C (250°F).

•	IAT less than 0°C (32°F)

A/C Clutch Circuit Diagnosis should be used for diagnosing the electrical portion of the A/C compressor clutch circuit. When diagnosing the refrigerant portion of the HVAC system.

A scan tool will be used in diagnosing the system. The scan tool has the ability to read the A/C request and refrigerant pressure inputs to the PCM. The scan tool can display when the PCM has commanded the A/C clutch on. The scan tool should have the ability to override the A/C request signal and energize the A/C control relay.