Air Conditioning (A/C) Compressor Control Circuit Diagnosis. Buick Century (China) (CNG) 1999

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Engine 🢒 Engine Controls - 3.0L (L46) 🢒 Air Conditioning (A/C) Compressor Control Circuit Diagnosis

Refer to

HVAC and A/C Compressor Clutch Coil

Circuit Description

When A/C is selected through the A/C control head a signal is supplied to the PCM through the Class ll serial data circuit. The A/C compressor clutch relay is controlled through the PCM. 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 96%.

•	A/C head pressure greater than 440 psi (4.6 volts) or less than 35 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition voltage below 10 volts.

•	Engine speed greater than 4700 RPM.

•	ECT greater than 124°C (255°F).

•	IAT less than 5°C (41°F).

Step

Action

Value(s)

Yes

Was the Powerrtrain OBD System Test performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any PCM or HVAC DTCs stored?

Diagnose 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.
Turn the ignition switch to the on position (engine off).
Test for the engagement of the A/C clutch.

Is the A/C Clutch engaged?

Go to Step 13

Go to Step 4

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

Is the A/C clutch engaged?

Refer 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 - 4.6V

Go to Functional Check

Go to Step 7

Connect a J 39500-B Refrigerant Recovery, Recycling, and Recharging (ACR4) to monitor high side refrigerant pressure.
Observe high side refrigerant pressure on the J 39500-B Refrigerant Recovery, Recycling, and Recharging (ACR4) gauge.

Is high side refrigerant pressure within the specified values?

35 psi - 440 psi

Go to VDOT Air Conditioning (A/C) System Diagnosis

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

Inspect the A/C clutch fuse.

Is the A/C cutch fuse blown?

Go to Step 9

Go to Step 10

Remove the A/C clutch fuse.
Remove the A/C Relay.
Test 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 Repair Procedures in Wiring Repairs .

Was a problem found?

Go to Step 18

Go to Step 15

Remove the A/C relay.
Connect a 10A 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

Test 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 Repair Procedures in Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs .

Was a problem found?

Go to Step 18

Go to Step 15

Test for poor terminal connections in the A/C Relay in the
Underhood Accessory Wiring Junction Block (RPO L82)

.
If a problem is found, repair as necessary. Refer to Repair Procedures in Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and 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 clutch. Refer to Compressor Clutch Plate and Hub Assembly Removal .

Is the action complete?

Go to Step 18

Replace the A/C relay. Refer to Compressor Relay Replacement .

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 Repair Procedures in Wiring Repairs .

Is th 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 engaged and disengage?

System OK

Go to Step 3

HVAC and A/C Compressor Clutch Coil

Circuit Description

Underhood Accessory Wiring Junction Block (RPO L82)