Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis. Buick Regal 1998

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1998 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Table 1:

A/C Clutch Control Circuit Diagnosis

Refer to HVAC Schematic HVAC Compressor Control Schematics C60 and CJ3

Refer to HVAC System HVAC Compressor Control Schematics CJ2

Circuit Description

When A/C is selected through the A/C control head a signal is supplied to the PCM A/C request circuit through the Class II serial data circuit on vehicle with CJ2 systems, on vehicles with C60 and CJ3 systems the A/C control head supplies the signal to the PCM A/C request circuit. The A/C 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 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 positive 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:

VIN K

•	Throttle angle is greater than 96%.

•	A/C head pressure is greater than 440 psi (4.6 volts) or less than 32 psi (0.3 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition 1 voltage is below 9.5 volts.

•	Engine speed is greater than 4392 RPM for less than 1 second.

•	Engine speed is greater then 4400 RPM for any amount of time.

•	ECT is greater than 124°C (255°F).

•	IAT is less than 5°C (41°F).

VIN 1

•	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 9.5 volts.

•	Engine speed is greater then 4392 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:

VIN K

•	Throttle angle is greater than 96%.

•	A/C head pressure is greater than 440 psi (4.6 volts) or less than 32 psi (0.3 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition 1 voltage is below 9.5 volts.

•	Engine speed is greater than 4392 RPM for less than 1 second.

•	Engine speed is greater then 4400 RPM for any amount of time.

•	ECT is greater than 124°C (255°F).

•	IAT is less than 5°C (41°F).

VIN 1

•	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 9.5 volts.

•	Engine speed is greater then 4392 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 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?

Go to 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?

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 - 4.6V

Go to System Performance Test

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 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 (V5 - Direct Mount) or Compressor Clutch Plate and Hub Assembly Removal (V5 - Conventional Mount) in HVAC System.

Is the action complete?

Go to Step 18

Replace the A/C relay.

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 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 engaged and disengage?

System OK

Go to Step 3

A/C Clutch Control Circuit Diagnosis

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any PCM or HVAC DTC(s) stored?

Diagnose the applicable DTC(s). Go to Diagnostic Trouble Code (DTC) List

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 OFF the A/C Selector Switch.
Ignition ON, engine OFF.
Listen for engagement of the A/C clutch.

Is the A/C Clutch engaged?

Go to Step 25

Go to Step 4

Run the engine at 1000 - 1500 RPM.
Select A/C mode on the HVAC Control Head.
Observe A/C compressor.

Is the A/C compressor clutch engaged?

Go to Diagnostic Aids

Go to Step 5

With the A/C mode still selected, observe the A/C Request display on the scan tool.

Does the A/C Request display YES?

Go to Step 12

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 to monitor high side refrigerant pressure.
Observe high side refrigerant pressure on the gauge.

Is high side refrigerant pressure within the specified values?

35 psi - 440 psi

Go to Step 8

Go to Refrigerant Recovery and Recharging

Turn OFF the ignition switch.
Disconnect the PCM and the A/C refrigerant pressure sensor.
Measure the resistance of the following circuits between the PCM and the A/C Refrigerant Pressure Sensor:

•	A/C refrigerant pressure sensor signal circuit.

•	5 Volt Reference B circuit.

•	Sensor Ground circuit.

If any resistance is higher than the specified value, locate and repair cause of high resistance in the circuit as necessary. Refer to Wiring Repairs .

Was a problem found?

5 ohms

Circuit Description

Diagnostic Aids

Underhood Accessory Wiring Junction Block (RPO L82)

A/C Clutch Control Circuit Diagnosis