Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis. Buick Park Avenue 1997

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1997 🢒 Park Avenue 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Engine Controls Components
PCM Fuel Pump and Boost Solenoid VIN 1
OBD II Symbol Description Notice

Circuit Description

When an A/C mode is selected, the HVAC system sends a serial data message to the PCM requesting A/C compressor operation. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C compressor relay is engaged battery voltage is supplied to the compressor clutch coil. The PCM will enable the A/C compressor clutch whenever the engine is running and A/C has been requested unless one or more of the following conditions are present:

•	Throttle angle is greater than 90%.

•	A/C head pressure is 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 is below 10.5 volts.

•	Engine speed is greater than 4500 RPM for longer than 5 seconds.

•	Engine speed is greater than 5400 RPM for any amount of time.

•	ECT is greater than 125°C (257°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, A/C compressor, A/C control head, A/C relay, or A/C refrigerant pressure sensor.

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:

•	Throttle angle 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 1 voltage less than 10.5 volts.

•	Engine speed greater than 4500 RPM for longer than 5 seconds.

•	Engine speed greater than 5400 RPM for any amount of time.

•	ECT greater than 125°C (257°F).

•	IAT less than 5°C (41°F).

Test Description

Number(s) below refer to Step number(s) on the diagnostic table:

Stored diagnostic trouble codes 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 not be engaged with the engine running if an A/C mode is not selected.

The A/C compressor clutch should engage if the appropriate conditions are met and an A/C mode is selected.

Checks the ignition positive voltage circuits to the A/C relay.

Determines whether the condition is caused by a malfunctioning A/C relay.

Determines if the PCM is turning the A/C relay ON due to a command from the HVAC system.

Determines if the A/C relay is malfunctioning or if the A/C relay control circuit is grounded all the time.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

A/C Compressor Clutch Control Circuit Diagnosis

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

Are any Powertrain or HVAC DTC(s) stored?

Diagnose DTC(s) first.

Go to Step 3

Important: Before continuing with diagnosis, the following conditions must be met:

•	Ambient temperature greater than 9°C (48°F).

•	Engine coolant temperature less than 119°C (246°F).

With the A/C OFF, start and idle the engine.
Observe the A/C compressor.

Is the A/C compressor clutch engaged?

Go to Step 18

Go to Step 4

Run the engine at 1000-1500 RPM.
Select an A/C mode on HVAC control head.
Observe the A/C compressor.

Is the A/C compressor clutch engaged?

Refer to Diagnostic Aids

Go to Step 5

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

Does A/C Request display Yes?

Go to Step 9

Go to Step 6

Observe A/C High Side Pressure on the scan tool.

Is indicated A/C High Side Pressure between the specified values?

0.35-4.27V

Go to A/C Controls Diagnosis in Heater, Ventilation, And Air Conditioning

Go to Step 7

Connect a J 39500 Refrigerant Recovery, Recycling, and Recharging Station to monitor high side refrigerant pressure. Refer to Heater, Ventilation and Air Conditioning .
Observe high side refrigerant pressure on the gauge.

Is high side refrigerant pressure within the specified values?

234-2854 kPa

(34-414 psi)

Go To Step 8

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

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 circuit as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

5 ohms

Go to Step 31

Go to Step 15

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

Is the test light ON?

Go to Step 10

Go To Step 25

Connect a fused jumper between the ignition positive voltage circuit and A/C compressor clutch control circuit (CKT 59) at the A/C compressor relay connector.

Does the A/C compressor clutch engage?

Go to Step 11

Go to Step 12

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

Was a problem found?

Go to Step 31

Go to Step 26

Disconnect the A/C compressor clutch electrical connector (leave the ignition positive voltage 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 control circuit (CKT 59) and the compressor ground circuit.

Is the test light ON?

Go to Step 13

Go to Step 14

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

Was a problem found?

Go to Step 31

Go to Step 27

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. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

Go to Step 31

Go to Step 28

Leave the PCM and the A/C refrigerant pressure sensor disconnected.
Turn ON the ignition switch.
Using a J 39200 Digital Multimeter, measure voltage between the A/C refrigerant pressure signal circuit and ground.

Does the voltage measure near the specified value?

0 V

Go to Step 16

Go to Step 17

Check for the following conditions:

•	The 5 volt reference B circuit for a poor connection at the PCM.

•	The 5 volt reference B circuit for a poor connection at the A/C refrigerant pressure sensor.

•	The A/C refrigerant pressure signal circuit for a poor connection at the PCM.

•	The A/C refrigerant pressure signal circuit for a poor connection at the A/C refrigerant pressure sensor.

•	The sensor ground circuit for a poor connection at the A/C refrigerant pressure sensor.

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

Was a problem found?

Go to Step 31

Go to Step 30

Locate and repair short to voltage in the A/C refrigerant pressure signal circuit. Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?

Go to Step 31

Ensure that the A/C is OFF.
Observe A/C Request on the scan tool.

Does A/C Request display Yes?

Go to A/C Controls Diagnosis in Heater, Ventilation, and Air Conditioning

Go To Step 19

Disconnect the A/C compressor relay.
Start the vehicle.
Observe the A/C compressor.

Is the A/C compressor clutch engaged?

Go to Step 23

Go to Step 20

Probe the A/C compressor relay control circuit at the A/C compressor relay harness connector with a test light to B+.

Is the test light ON?

Go to Step 21

Go to Step 26

Turn OFF the ignition switch.
Disconnect the PCM.
Probe the A/C compressor relay control circuit at the PCM connector with a test light connected to B+.

Is the test light ON?

Go to Step 22

Go to Step 29

Repair short to ground in the A/C compressor relay control circuit. Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?

Go to Step 31

Turn OFF the ignition switch.
Disconnect the A/C compressor clutch electrical connector.
Start the engine.
Observe the A/C compressor.

Is the A/C compressor clutch engaged?

Go To Step 27

Go to Step 24

Locate and repair short to voltage in the A/C compressor clutch control circuit (CKT 59). Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?

Go to Step 31

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

Is action complete?

Go to Step 31

Replace the A/C compressor relay.

Is action complete?

Go to Step 31

Repair the A/C compressor clutch. Refer to V5 Air Conditioning Compressor Service.

Is action complete?

Go to Step 31

Locate and repair open in the A/C compressor clutch ground circuit (CKT 450).

Is action complete?

Go to Step 31

Replace the PCM.

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

Is action complete?

Go to Step 31

Replace the A/C refrigerant pressure sensor. Refer to On-Vehicle Service in Heater, Ventilation and Air Conditioning.

Is action complete?

Go to Step 31

Important: Before continuing with diagnosis, the following conditions must be met:

•	Ambient temperature greater than 9°C (48°F).

•	Engine coolant temperature less than 119°C (246°F).

With the A/C OFF, start and idle the engine.

Is the A/C compressor clutch engaged?

Go to Step 18

Go to Step 32

Run the engine at 1000-1500 RPM.
Select an A/C mode on HVAC control head.
Observe A/C compressor.

Is the A/C compressor clutch engaged?

System OK

Go to Step 5