For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: HVAC Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Start the engine.
2. Turn the blower switch to any position except OFF.
3. Press the A/C switch to the ON position.

Does the A/C compressor clutch engage?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Connect a scan tool.
2. Use the scan tool to command the A/C compressor clutch relay ON. When the relay is energized the cooling fan will also run at low speed.

Does the A/C compressor clutch engage?

Go to Step 8

Go to Step 4

4 |

1. Exchange the A/C compressor clutch relay with a known good relay.
2. Use the scan tool to command the A/C compressor clutch relay ON.

Does the A/C compressor clutch engage?

Go to Step 16

Go to Step 5

5 | Test the A/C compressor clutch supply voltage circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 6
6 |

1. Remove the A/C compressor clutch relay from the underhood fuse block.
2. Start the engine and turn the blower switch to any position except OFF.
3. Test for supply voltage to the A/C compressor clutch relay. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 7

7 | Test the A/C compressor clutch relay control circuit for an open or a short to B+. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 20
8 | Test the A/C switch supply voltage circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 9
9 | Test the A/C request circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 10
10 |

1. Start the engine.
2. Turn the blower switch to any position except OFF.
3. Press the A/C switch to the ON position.
4. Measure the voltage at cavity 9 of the A/C switch. The voltage should be 12.5 volts.

Is the measured voltage within specification?

Go to Step 11

Go to Step 18

11 | Measure the resistance of the A/C resistor. The resistance should be 2.2K ohms. Is the measured resistance within specification? | Go to Step 12 | Go to Step 25
12 | Test the A/C resistor feed and ground circuits for an open, a short to ground and for a short to B+. Any one of these conditions will cause the A/C system to be inoperative. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 13
13 |

• | Test the refrigerant pressure switch signal circuit for an open or a short to B+. Refer to Circuit Testing and Wiring Repairs .

• | Test the fan 2 coil control circuit for an open or a short to B+. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 14

14 | Test the refrigerant pressure switch ground circuit for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 15
15 | Test the refrigerant pressure switch. The switch should be normally closed . Did the switch test OK? | Go to Step 20 | Go to Step 19
16 | Inspect for a poor connection at the harness connector of the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 17 | Go to Step 21
17 | Inspect for a poor connection at the harness connector of the A/C compressor clutch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 22
18 | Inspect for a poor connection at the harness connector of the A/C switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 23
19 | Inspect for a poor connection at the harness connector of the refrigerant pressure switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 24
20 | Inspect for a poor connection at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 27 | Go to Step 26
21 | Replace the A/C compressor clutch relay. Did you complete the replacement? | Go to Step 27 | --
22 | Replace the A/C compressor clutch. Did you complete the replacement? | Go to Step 27 | --
23 | Replace the A/C switch. Did you complete the replacement? | Go to Step 27 | --
24 | Replace the refrigerant pressure switch. Did you complete the replacement? | Go to Step 27 | --
25 | Replace the A/C resistor. Did you complete the replacement? | Go to Step 27 | --
26 | Replace the engine control module (ECM). Did you complete the replacement? | Go to Step 27 | --
27 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3