For 1990-2009 cars

Table 1: | Compressor Control Module Voltage Table

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: HVAC Schematics
1 | Did you review the Air Delivery Description and Operation and the Air Temperature Description and Operation and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - HVAC Systems - Manual
2 |

1. Connect a scan tool.
2. Turn the blower switch to any position except OFF.
3. Press the A/C switch to the ON position.
4. Use the scan tool to command the A/C compressor clutch (MG) relay ON. When the MG relay is energized the cooling fans will also run at low speed.

Does the A/C compressor clutch engage?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3 |

1. Exchange the A/C MG relay with a known good relay (the fan 1, the fan 3 or the horn relay).
2. Turn the blower switch to any position except OFF.
3. Press the A/C switch to the ON position.
4. Use the scan tool to command the A/C compressor clutch (MG) relay ON.

Does the A/C compressor clutch engage?

Go to Step 15

Go to Step 4

4 |

1. Disconnect the A/C compressor clutch connector.
2. Connect a test lamp across the connector.
3. Press the A/C switch to the ON position.
4. Turn the blower switch to any position except OFF.
5. Use the scan tool to command the A/C compressor clutch (MG) relay ON.

Does the test lamp illuminate?

Go to Step 16

Go to Step 5

5 | Test the A/C compressor clutch ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 6
6 | Test the A/C compressor clutch supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 7
7 |

1. Remove the A/C MG relay from fuse and relay block 2.
2. Start the engine and turn the blower switch to any position except OFF.
3. Test for supply voltage to the A/C MG relay at cavities 1 and 5. Refer to

   #### Fuse and Relay Block 2

   (1) | A/C MG Relay
   (2) | A/C FAN No.3 Relay
   (3) | A/C FAN No.3 Relay
   (4) | Dimmer Relay
   (5) | CDS Fuse 30A
   (6) | HEAD (LH-LWR) Fuse 10A
   (7) | HEAD (RH-LWR) Fuse 10A
   (8) | DRL Fuse 7.5A
   (9) | Fuse and Relay Block 2

   , Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 8

8 | Test the A/C MG relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 9
9 | Test the A/C compressor control module supply voltage circuit (including the A/C switch) for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Refer to Control Assembly Replacement for A/C switch replacement. Did you find and correct the condition? | Go to Step 21 | Go to Step 10
10 | Test the A/C compressor control module ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 11
11 | Test the A/C refrigerant pressure switch circuit and the switch for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems and Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement . Did you find and correct the condition? | Go to Step 21 | Go to Step 12
12 | Test for a short to ground in the BLU/WHT wire between the underhood data link connector terminal 8 (TE 1) and the PCM connector 2 terminal 15. Grounding this circuit puts the vehicle in diagnostic request mode and will prevent the A/C from operating when the engine speed is below 1200 RPM.

Did you find and correct the condition?

Go to Step 21

Go to Step 13

13 | Test the A/C output control circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 14
14 | Test the A/C cutout signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 17
15 | Inspect for a poor connection at the fuse and relay block 2 connector of the A/C MG relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 18
16 | 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 in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 19
17 | Inspect for a poor connection at the harness connector of the A/C compressor control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 20
18 | Replace the MG relay. Refer to Compressor Relay Replacement . Did you complete the replacement? | Go to Step 21 | --
19 | Replace the A/C compressor clutch. Refer to Compressor Clutch Plate and Hub Assembly Removal , Air Conditioning Clutch Coil Removal , Air Conditioning Clutch Coil Installation and Compressor Clutch Plate/Hub Assembly Install . Did you complete the replacement? | Go to Step 21 | --
20 | Replace the A/C compressor control module. Refer to Air Conditioning (A/C) Compressor Control Module Replacement . Did you complete the replacement? | Go to Step 21 | --
21 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3

#### Compressor Control Module Voltage Table

Terminal-Wire Color | Circuit | Normal Voltage | Condition
--- | --- | --- | ---
1-YEL/BLU | Refrigerant Pressure Switch | B+ | Ignition switch ON
2 | Not Used
3-RED/BLU | A/C Cutout Signal (WOT) | 0-1 Volts | Ignition Switch ON, A/C Switch OFF
10-14 Volts | Engine Running, A/C Operating
4-WHT/BLU | Ground | 0-1 Volts | Ignition switch ON
5-YEL | Ignition Positive Voltage | B+ | Ignition Switch ON, A/C Switch ON or Defrost Switch ON
6-7 | Not Used
8-YEL/RED | A/C ON Output Control | 10-14 Volts | Ignition Switch ON, A/C Switch OFF
0-1 Volts | Engine Running, A/C Operating
9-BLU/BLK | A/C MG Relay Control | B+ | Ignition Switch ON, A/C Switch OFF
0-1.5 Volts | Engine Running, A/C Operating
10 | Not Used