For 1990-2009 cars

### Circuit Description

The Compressor Controls System Check is an organized approach to identify problems associated with the heater & A/C control. This check must be the starting point for any compressor controls complaint, and will direct you to the next logical step in diagnosing the complaint. The heater and A/C control is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring and connectors, and occasionally to components. Understanding the computer system and using the tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

### Diagnostic Aids

The following conditions may result in an intermittent operation of the heater and A/C control with no DTC stored:

• | Any condition which results in the interruption of power to the heater and A/C control.

• | Out of range battery or ignition voltage

Specification
Normal operating voltage: 9.0-16.0 V

• | A loose or damaged ground(s)

• | An open or shorted serial data line

• | An intermittent failure in the electronic system may be very difficult to detect and to accurately diagnose. A good description of the complaint may be very useful in locating an intermittent malfunction. Faulty electrical connections or wiring causes most intermitting problems. When an intermitting condition is suspected, check the suspected circuits for the following conditions:

- | Poor mating of connector halves or backed out terminals

- | Improperly formed or damaged terminals

- | Wire chafing

- | Poor wire to terminal connections

- | Dirty or corroded terminals

- | Damage to connector bodies

• | If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Perform a thorough inspection of all related wiring and connectors pertaining to the history DTC stored.

• | Exit all scan tool tests before cycling the ignition OFF to ON unless the scan tool instructions direct otherwise. Follow the operating instructions in the scan tool operator's manual. Failure to follow these instruction may set DTCs, cause vehicle system malfunctions, set false DTCs, or cause scan tool malfunctions.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. This step checks the functionality of the complete A/C system.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 |

1. Connect the scan tool to the Data Link Connector (DLC).
2. Attempt to establish communications with the heater and A/C control.

Does the scan tool display data?

--

Go to Step 2

Go to Step 5

2 | Are any current DTCs displayed? | -- | Go to Applicable DTC Table | Go to Step 3
3 | Are any history or intermittent DTCs displayed? | -- | Go to Step 4 | Go to Step 6
4 | Refer to Diagnostic Aids of the DTC that is displayed. Try to perform the tests shown while "wiggling" wiring and connectors, this can often can cause the malfunction to occur. Was a problem found and repaired? | -- | System OK | --
5 | Refer to Scan Tool Does Not Communicate With Heater and A/C Control. Go to Data Link Connector in Wiring Systems for diagnostic table. Was a repair made? | -- | Go to Step 1 | --
6 |

1. Remove the scan tool.
2. Start the engine and let it reach operating temperature.
3. Turn On the air conditioning by pressing the A/C button on the heater & A/C control.
4. Select 16°C (60°F) and maximum blower speed.

Does the compressor operate?

--

System OK

Go to Step 7

7 | Refer to A/C Compressor Controls Circuit Diagnosis in Engine Controls. Was a repair made and does the compressor operate properly? | -- | System OK | --