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

- | A loose or damaged grounds

• | 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.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. A current DTC P1545 may inhibit the A/C compressor clutch from engaging.

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 DTC Table | Go to Step 3
3 | Are any history or intermittent DTCs displayed? | -- | Go to Step 4 | Go to Step 6
4 |

1. Refer to the Diagnostic Aids of the DTC that is displayed.
2. Try performing the tests listed of that particular DTC while moving the harness wiring and connectors, this can often cause the malfunction to occur.

Was a problem found and repaired?

--

System OK

--

5 | Refer to Scan Tool Does Not Communicate with Heater and Air Conditioning (A/C) Control in Wiring System. Was a repair made? | -- | Go to Step 1 | --
6 |

1. With the scan tool establish communications with the engine control module (ECM).
2. Select DTC information.

Is a current DTC P1545 (A/C Clutch Relay Control Circuit) set?

--

Go to Step 7

Go to Step 8

7 | Refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls in order to navigate to the DTC diagnosis. Was a problem found and repaired? | -- | Go to Step 8 | --
8 |

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?

--

Go to Step 9

Go to Cooling Insufficient - Air Conditioning (A/C) Inoperative

9 | Verify that the A/C system cools properly. Is the A/C system operating properly? | -- | System OK | Go to System Performance Test