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

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Alero Export 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Air Conditioning (A/C) Compressor Control Circuit Diagnosis

Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

When an A/C mode is selected, the A/C control head or the Body Function Controller (BFC) supplies a signal to the PCM through the Class II Serial Data Circuit. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C compressor relay is engaged 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 one or more of the following conditions are present:

•	Throttle angle is greater than 96%.

•	A/C head pressure is greater than 440 psi (4.6 volts) or less than 35 psi (0.4 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition 1 voltage is below 10.5 volts.

•	Engine speed is greater than 4300 RPM for longer than 1 second.

•	Engine speed is greater then 5400 RPM for any amount of time.

•	ECT is greater than 124°C (255°F).

•	IAT is less than 5°C (41°F).

Any of the conditions described above will inhibit A/C compressor relay operation.

Diagnostic Aids

Check for the following conditions:

•	Poor connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

•	Damaged harness. Inspect the wiring harness for damage.

•

If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a voltmeter connected to the A/C relay control circuit at the PCM harness connector while moving connectors and wiring harnesses related to the A/C relay. A change in voltage will indicate the location of the malfunction.

Check for conditions that will disable A/C operation:

•	Throttle angle is greater than 96%.

•	A/C head pressure is greater than 440 psi (4.6 volts) or less than 35 psi (0.4 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition 1 voltage is below 10.5 volts.

•	Engine speed is greater than 4300 RPM for longer than 1 seconds.

•	Engine speed is greater then 5400 RPM for any amount of time.

•	ECT is greater than 124°C (255°F).

•	IAT is less than 5°C (41°F).

Step

Action

Value(s)

Yes

Was the Powertrain On-board-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any PCM or BFC DTCs stored?

Go to The Applicable DTCs

Go to Step 3

Important: : The following conditions must be met before continuing with this step:

•	Ambient air temperature must be above 5°C (41°F).

•	A/C Pressure must be above 35 PSI (0.4 volts).

•	Coolant temperature must be below 121°C (250°F).

Turn the A/C Selector Switch to the OFF position.
Start and Idle the engine.
Check for the engagement of the A/C clutch.

Is the A/C Clutch engaged?

Go to Step 13

Go to Step 4

Operate the engine at 1000 - 1500 RPM.
Turn the A/C selector switch to an A/C mode.
Observe the A/C clutch.

Is the A/C clutch engaged?

Go to Diagnostic Aids

Go to Step 5

Leave the A/C selector switch turned to an A/C mode.
Observe the A/C Request display on the scan tool.

Does the A/C Request display YES?

Go to Step 8

Go to Step 6

Observe the A/C pressure sensor display on the scan tool.

Does the A/C pressure sensor indicate a voltage between the specified values?

0.4V - 4.2V

Go to Functional Check

Go to Step 7

Connect a J 39500 Refrigerant Recovery, Recycling, and Recharging Station to monitor high side refrigerant pressure. Refer to Refrigerant Recovery and Recharging .
Observe high side refrigerant pressure on the gauge.

Is the high side refrigerant pressure within the specified values?

35 psi - 440 psi

Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit

Go to Refrigerant Recovery and Recharging

Check the A/C clutch fuse.

Is the A/C Clutch fuse blown?

Go to Step 9

Go to Step 10

Remove the A/C clutch fuse.
Remove the A/C relay.
Check for the following circuit condition(s):

•	Short to ground in the battery positive feed to the A/C relay.

•	Short to ground in the battery positive feed to the A/C clutch.

•	Shorted diode.

If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

Go to Step 18

Go to Step 15

Remove the A/C relay.
Connect a 10 A fused jumper between the battery positive and A/C clutch coil feed cavities in the A/C relay connector.

Is the A/C clutch engaged?

Go to Step 12

Go to Step 11

Check for the following circuit condition(s):

•	Open in the battery positive feed circuit to the A/C relay.

•	Open in the battery positive feed circuit to the A/C clutch.

•	Open in the A/C clutch ground circuit.

•	Poor terminal connections in the A/C clutch coil connector.

If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

Go to Step 18

Go to Step 15

Check for poor terminal connections in the A/C relay connector.
If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

Go to Step 18

Go to Step 16

Turn the ignition switch to the OFF position.
Remove the A/C relay.
Turn the ignition switch to the ON position.

Is the A/C clutch engaged?

Go to Step 14

Go to Step 16

Disconnect the A/C clutch connector.

Is the A/C clutch engaged?

Go to Step 15

Go to Step 17

Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .

Is the action complete?

Go to Step 18

Replace the A/C relay. Refer to Electrical Center Identification Views in Wiring Systems.

Is the action complete?

Go to Step 18

Locate and repair the short to voltage in the battery positive feed circuit to the A/C clutch. Refer to Wiring Repairs .

Is the action complete?

Go to Step 18

Important: : The following conditions must be met before continuing with this step:

•	Ambient air temperature must be above 5°C (41°F)

•	A/C pressure must be above 35 psi (0.4 volts)

•	Coolant temperature must be below 121°C (250°F)

Start and operate the engine between 1000-1500 RPM.
Turn the A/C selector switch to the ON position.
Listen for engagement of the A/C clutch.
Wait 5 seconds and then turn the A/C selector switch to the OFF position.
Listen for disengagement of the A/C clutch.

Did the A/C clutch engage and disengage?

System OK

Go to Step 3