For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC 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 14

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 24 | 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 24

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 24 | Go to Step 18
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 24 | 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 24 | 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 16

11 |

• | 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 24

Go to Step 12

12 | 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 24 | Go to Step 13
13 | Test the refrigerant pressure switch. The switch should be normally closed. Did the switch test OK? | Go to Step 18 | Go to Step 17
14 | 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? | Step 24 | Go to Step 19
15 | 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? | Step 24 | Go to Step 20
16 | 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? | Step 24 | Go to Step 21
17 | 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? | Step 24 | Go to Step 22
18 | 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? | Step 24 | Go to Step 23
19 | Replace the A/C compressor clutch relay. Did you complete the replacement? | Step 24 | --
20 | Replace the A/C compressor clutch. Did you complete the replacement? | Step 24 | --
21 | Replace the A/C switch. Did you complete the replacement? | Step 24 | --
22 | Replace the refrigerant pressure switch. Did you complete the replacement? | Step 24 | --
23 | Replace the engine control module (ECM). Did you complete the replacement? | Step 24 | --
24 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3