Air Conditioning (A/C) Compressor Control Circuit Diagnosis. Chevrolet Malibu 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Malibu 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 Air Conditioning (A/C) Compressor Control Circuit Diagnosis

Engine Controls Components
Cell 23: Transaxle Controls (Switches)
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Diagnosis

Refer to the Heating, Ventilation, and Air Conditioning section of the service manual for diagnosis of the refrigerant portion of the system.

A scan tool can be used to display the following parameters:

•	A/C Request--This displays if PCM has received an A/C request from Body Controll Module (BCM) YES or NO.

•	A/C Clutch--This displays if the PCM has commanded the A/C clutch ON or OFF.

•	A/C Highside--This displays the A/C refrigerant highside pressure in VOLTS and PSI .

The PCM receives an A/C request signal from the Body Control Moduel (BCM) over the Class 2 serial data line. When A/C is requested, the Powertrain Control Module (PCM) provides a ground path to the A/C clutch relay control circuit. When the relay circuit is grounded, the A/C compressor clutch relay is energized. The PCM delays grounding the relay circuit for .3 second, so the PCM can adjust the engine idle RPM for the additional load.

The PCM will temporarily de-energize the A/C compressor clutch relay for one or more of the following conditions:

•	A hot engine restart.

•	A wide open throttle (TP sensor over 90%).

•	Engine RPM greater than 6000 RPM.

•	During an Idle Air Control (IAC) valve reset.

The A/C compressor clutch relay will remain de-energized when one or both of the following conditions exist:

•	A DTC P0530 is set.

•	There is no A/C request signal to the PCM.

Refer to the Air Conditioning System section of the service manual for more information on the A/C refrigerant systems.

Diagnostic Aids

•	If DTCs P0530, U1000 or U1064 are set, do not use this table.

•	If the complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan. Refer to Electric Cooling Fan Diagnosis protion of the service manual.

•	If the fan operates correctly, refer to the Heating, Ventilation and Air Conditioning (HVAC) portion of the service manual for further diagnosis.

•

An A/C refrigerant pressure outside the range of 43 to 428 psi, will cause the A/C compressor clutch to be disabled by the PCM. Observe the A/C refrigerant pressure parameter on the scan tool for 2 minutes with the engine idling and A/C ON. If pressure goes out of range, refer to Air Conditioning System portion of the service manual for further diagnosis.

Test Description

The number(s) below refer(s) to the number(s) on the diagnostic table.

The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

The PCM will only energize the A/C relay when the engine is running or momentarily during cranking the engine in order to minimize the slugging noise. This step will determine if the relay or control circuit is malfunctioning.

By disconnecting the relay, the system can be divided into two sections. If the clutch does not disengage, the malfunction lies on the compressor side of the system.

This step determines if the signal is reaching the PCM from the A/C control panel from the Body Control Module (BCM). The signal should only be present when an A/C mode or a defrost mode has been selected and the blower motor is turned ON.

A test light that does not illuminate indicates that the A/C compressor clutch relay is malfunctioning.

This step determines if the system is normal or if the A/C refrigerant pressure sensor reading is out of range.

The A/C request signal is communicated through the Body Control Module (BCM) to the PCM over the Class 2 serial data line. The BCM also receives other information in order to decide if the A/C request should be enabled. This step checks for the A/C request switch for the correct function. Additional steps must be completed in order to perform this step correctly. The blower motor must be turned ON and the heater, the vent, and the A/C Control assembly (HVAC) selector switch must not be in the OFF position. With the A/C selector switch in the OFF position, the scan tool should read A/C request OFF. If the A/C selector switch is in the ON position, the scan tool may read Clutch enabled or the following conditions: OFF, Low RPM, - OFF, Low Ambient - OFF, High Press - OFF, Low Battery Voltage - OFF, High Coolant Temp. If any of the above conditions are present on the scan tool when the A/C selector switch is enabled, the BCM senses a change.

Connecting the ignition feed circuit and the A/C compressor Clutch feed circuit together bypasses the PCMs control of the A/C compressor clutch. An A/C compressor clutch that fails to engage at this point indicates that the malfunction is in the A/C Compressor Clutch feed circuit, the compressor coil, or the compressor coil ground circuit.

Locate and repair any shorts that may have caused the fuse to open before replacement.

With the engine running and the A/C relay commanded ON, the PCM should ground the A/C relay control circuit. This will also illuminate the test light.

Reprogram the replacement PCM and perform the crankshaft position system variation learning procedure. Refer to the latest Techline information for PCM programming and the Crankshaft Position System Variation Learn for the crankshaft position system variation learning procedure.

This step determines if the A/C refrigerant pressure sensor is out of range causing the A/C compressor clutch to be disabled or if the A/C charge is to low to allow A/C operation.

If no malfunctions are present at this point, refer to the Diagnostic Aids for additional checks and information.