Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis. Chevrolet Lumina 1996

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Lumina 🢒 Engine 🢒 Engine Controls - 3.4L (VIN X) 🢒 Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Refer to

HVAC A/C Control

Engine Controls Components
Powertrain Control Module Controlled Air Conditioning
Engine Cooing Fans
AIR ,Gen Control Volts Lamp, Low Oil
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

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:

•	TP angle greater than 95%

•	A/C head pressure greater than 440 psi or less than 36 psi (as determined by the A/C refrigerant pressure sensor).

•	Ignition voltage below 10 volts.

•	Engine speed greater than 4300 RPM.

•	ECT greater than 123°C (253°F).

•	IAT less than 5°C (41°F)

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 driver 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 fault.

Check for conditions that will disable A/C operation:

•	Throttle angle greater than 95%.

•	A/C head pressure greater than 440 psi or less than 36 psi (as determined by the A/C refrigerant pressure sensor).

•	Ignition voltage below 10 volts.

•	Engine speed greater than 430 RPM.

•	ECT greater than 123C (253F).

•	IAT less than 5°C (41°F).

Test Description

Number(s) below refer to circled number(s) on the diagnostic chart:

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 listed under the Important are 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.

Determines whether the A/C relay is faulty or the A/C relay driver circuit is grounded all the time.

A/C Clutch Control Circuit Diagnosis

Step

Action

Value(s)

Yes

Was the 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?

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

Is the A/C compressor clutch engaged?

Refer 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

Ignition OFF, disconnect the PCM.
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.

Was a problem found?

Go to Step 29

Go to Step 27

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

Is indicated A/C pressure between the specified values?

34 psi - 440 psi (0.4V - 4.6V)

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?

34 psi - 440 psi

(0.4V - 4.6V)

Go to Step 11

Go to Refrigerant Recovery and Recycling, Adding Oil, Evacuating and Recharging Procedures in Heater, Ventilation and Air Conditioning.

Ignition OFF, disconnect A/C Pressure sensor.
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 (0V)

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 J 35616-200 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 (CKT 59) 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 (CKT 59) jumpered at the A/C relay connector).
Connect a test light between A/C compressor clutch feed circuit (CKT 59) 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.

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 (CKT 59).
If a problem is found, repair as necessary.

Was a problem found?

Go to Step 29

Go to Step 26

Ignition ON
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

Ignition OFF.
Disconnect the PCM.
Ignition ON, A/C OFF.
Using a DVM, 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