Air Conditioning (A/C) Compressor Clutch Control Diagnosis. Buick Century 1997

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1997 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L 🢒 Air Conditioning (A/C) Compressor Clutch Control Diagnosis

Engine Controls Components
A/C Compressor Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

When A/C is selected through the A/C control head a 12 volt signal is supplied to the A/C request input of the PCM. 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 90%.

•	A/C head pressure greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

•	Ignition voltage below 10.5 volts.

•	Engine speed greater than 4500 RPM for 5 seconds or 5400 RPM.

•	ECT greater than 125°C (257°F).

•	IAT less than 5°C (41°F).

Test Description

The numbers below refer to numbers on the Diagnostic Table.

The A/C compressor clutch should not be engaged with the engine running if an A/C mode is not selected at the control head.

Stored Diagnostic Trouble Codes (That may not illuminate the Malfunction indicator Lamp) may disable the A/C compressor. This Diagnostic Table may lead to improper diagnosis and replacement of good parts if Diagnostic Trouble Codes are present.

The A/C compressor clutch should apply if the conditions under the Notice have been met.

Checks for an A/C request signal from the control head to the PCM.

Checks the ignition feed circuit to the A/C relay.

Determines whether the A/C relay or the circuitry is at fault.

Determines whether or not the PCM is turning the A/C relay on due to a false A/C request.

Isolates problem to the A/C control head or the PCM.

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 DTC(s) stored?

Go to applicable DTC(s) Refer to Powertrain Control Module Diagnosis

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 36°C (96°F).

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

A/C selector switch off.
Turn the ignition on, engine off.
Listen for engagement of the A/C clutch.

Is the A/C Clutch engage.

Go to Step 18

Go to Step 4

Start the engine.
Select Defrost or MAX mode on HVAC control head.
Observe A/C compressor.

Is the A/C compressor clutch engaged?

Go to Diagnostic Aids

Go to Step 5

With Defrost or Max mode selected, monitor A/C Request display on the scan tool Engine data list.

Does A/C Request display Yes?

Go to Step 9

Go to Step 6

Turn the ignition off, disconnect the PCM.
Turn the ignition on.
With Defrost or Max mode selected, measure voltage on the A/C request circuit at the PCM harness connector.

Does the voltage measure near the specified value?

B+

Go to Step 8

Go to Step 7

Check the A/C request circuit for the following conditions:

•

Open.

•	Shorted to ground.

•	Poor connection at the A/C control head or A/C programmer (as applicable).

If a problem is found, repair as necessary.

Was a problem found?

Go to Step 29

Go to Electrical Diagnosis for A/C Controls diagnostics

Check the A/C request circuit for a poor connection at the PCM.
If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 29

Go to Step 27

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

Is A/C pressure indicated between the specified values?

36 - 440 psi

Go to Step 12

Go to Step 10

Connect J 39183-C R-134a Manifold gauge set. Refer to Heater, Ventilation and Air Conditioning.
Observe high side refrigerant pressure on the gauge.

Is high side refrigerant pressure within the specified values?

36 - 440 psi

Go to Step 11

Go to Refrigerant Recovery and Recharging Procedures in Heater, Ventilation and Air Conditioning

Turn the ignition off, disconnect the A/C Pressure sensor.
Turn the ignition on.
View A/C Highside display on the scan tool Engine data list.

Does the scan tool display an A/C Highside pressure at the specified value?

0 psi

Go to Step 28

Go to Step 27

Disconnect the A/C relay electrical connector.
Probe the ignition feed circuits at the A/C relay harness connector with a test light to ground.

Is the test light on?

Go to Step 13

Go to Step 23

Connect a fused jumper between the ignition feed circuit and A/C compressor clutch control circuit at the A/C relay connector.

Does the A/C compressor clutch engage?

Go to Step 14

Go to Step 15

Check for poor connections at A/C relay.
If a problem is found, replace faulty terminals as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 29

Go to Step 24

Disconnect the A/C compressor clutch electrical connector (leave the ignition control circuit and A/C compressor clutch control circuit jumpered at the A/C relay connector).
Connect a test light between A/C compressor clutch feed circuit and the compressor ground circuit.

Is the test light on?

Go to Step 16

Go to Step 17

Check for poor connections at the A/C compressor clutch.
If a problem is found, replace faulty terminals as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 29

Go to Step 25

Check for an open or short to ground in the A/C compressor clutch control circuit.
If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 29

Go to Step 26

Turn the ignition on.
Turn the A/C off.
Observe A/C Request display on the scan tool.

Does A/C Request display Yes?

Go to Step 19

Go to Step 21

Turn the ignition off.
Disconnect the PCM.
Turn the ignition on, turn the A/C off.
Using a DMM, measure voltage between the A/C request circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

B+

Go to Step 20

Go to Step 27

Turn the ignition off, disconnect the A/C control head.
Turn the ignition on. check the A/C Request circuit for a short to battery positive voltage.

If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 29

Go to Electrical Diagnosis for A/C Controls diagnostics

Disconnect the A/C relay.
Start the vehicle and observe the A/C compressor.

Is the A/C compressor clutch engaged?

Go to Step 22

Go to Step 24

Locate and repair short to voltage in the A/C compressor clutch control circuit. Refer to Repair Procedures in Electrical Diagnosis.

Is the action complete?

Go to Step 29

Repair open or short to ground in ignition feed circuit to the A/C compressor relay. Refer to Repair Procedures in Electrical Diagnosis.

Is the action complete?

Go to Step 29

Replace the A/C compressor relay.

Is the action complete?

Go to Step 29

Repair A/C compressor clutch. Refer to Air Conditioning Compressor Service.

Is the action complete?

Go to Step 29

Locate and repair open in A/C compressor clutch ground circuit.

Is the action complete?

Go to Step 29

Replace the PCM.

Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

Go to Step 29

Replace A/C refrigerant pressure sensor.

Is the action complete?

Go to Step 29

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 36°C (96°F).

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

Ignition on, engine running.
Turn A/C selector switch on.
Listen for engagement of the A/C clutch.

Is the A/C Clutch engage.

System OK

Go to Step 3