Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis. Buick Regal 1999

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1999 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Table 1:	A/C Clutch Control Circuit Diagnosis CJ2 Only
Table 2:	A/C Clutch Control Circuit Diagnosis C60 and CJ3 Only

Refer to HVAC Compressor Control Schematics C60 and CJ3 in HVAC System-Manual or HVAC Compressor Control Schematics CJ2 in HVAC System-Automatic.

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).

A/C Clutch Control Circuit Diagnosis CJ2 Only

Step

Action

Value(s)

Yes

Was the Powertrain 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 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 circuit.
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 C60 and CJ3 Only

Step

Action

Value(s)

Yes

Was the Powertrain 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 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 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 in HVAC System

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 in HVAC System

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 in Wiring Systems.

Was a problem found?

5 ohms