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For 1990-2009 cars only

HVAC Compressor Clutch Does Not Disengage 7.8L

Test Description

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

  1. Placing the blower motor switch in the OFF position and the mode switch to the floor position, disables an A/C request.

  2. The A/C compressor clutch relay must be disconnected from previous step. The A/C compressor clutch control circuit is wired between the A/C high pressure switch and the A/C compressor clutch relay.

  3. The A/C compressor clutch control circuit is wired between the A/C high pressure switch and the A/C compressor clutch relay.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: A/C compressor clutch will not disengage when an A/C request has not been made and a Powertrain DTC has not been set.

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Start the engine.
  2. Place the blower motor switch in the OFF position.
  3. Place the mode switch in the floor position.

Does the A/C compressor operate?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Start the engine.

Does the A/C compressor clutch disengage?

 

Go to Step 4

Go to Step 7

4

  1. Turn OFF the ignition.
  2. Measure the resistance of the switch side contacts of the A/C compressor clutch relay.

Does the resistance measure near the specified value?

Go to Step 5

Go to Step 10

5

  1. Start the engine.
  2. Probe the A/C compressor clutch control circuit of the A/C compressor clutch relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

 

Go to Step 6

Go to Step 10

6

  1. Turn OFF the ignition.
  2. Disconnect the A/C high pressure switch.
  3. Start the engine.
  4. Probe the A/C compressor clutch control circuit of the A/C compressor clutch relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

 

Go to Step 8

Go to Step 9

7

Test the A/C compressor clutch supply voltage circuit of the A/C compressor clutch for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 14

8

Test the A/C compressor clutch relay control circuit of the A/C compressor clutch relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 11

9

Test the A/C request signal circuit of the HVAC control assembly for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 12

10

Inspect for poor connections at 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 13

11

Inspect for poor connections at the harness connector of the engine control module (ECM). 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 15

12

Inspect for poor connections at the harness connector of the HVAC control assembly. 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 16

13

Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement .

Did you complete the replacement?

--

Go to Step 17

--

14

Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .

Did you complete the replacement?

--

Go to Step 17

--

15

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

 

Go to Step 17

 

16

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

--

Go to Step 17

--

17

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3

HVAC Compressor Clutch Does Not Disengage 6.6L, 8.1L

Test Description

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

  1. Placing the blower motor switch in the OFF position and the mode switch to the floor position, disables an A/C request.

  2. There are 2 A/C request signal circuits of the A/C high pressure switch. Both must be tested or misdiagnosis could occur.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: A/C compressor clutch will not disengage when an A/C request has not been made and a powertrain DTC has not been set.

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Start the engine.
  2. Place the blower motor switch in the OFF position.
  3. Place the mode switch in the FLOOR position.

Does the A/C compressor operate?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

  1. Turn ON the ignition.
  2. With a scan tool, observe the A/C Request Signal parameter in the Powertrain Engine Data list.

Does the scan tool indicate that the A/C Request parameter is YES?

--

Go to Step 4

Go to Step 6

4

Test both of the A/C request signal circuits of the A/C high pressure switch for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the A/C high pressure switch.
  3. Start the engine.
  4. Place the blower motor switch in the OFF position.
  5. With a scan tool, observe the A/C Request Signal parameter.

Does the scan tool indicate that the A/C Request parameter is YES?

--

Go to Step 12

Go to Step 11

6

Remove the A/C compressor clutch relay.

Does the A/C compressor clutch turn OFF?

--

Go to Step 7

Go to Step 9

7

Measure the resistance between the switch side A/C compressor clutch relay terminals at the relay.

Does the resistance measurement equal the specified value?

Go to Step 8

Go to Step 10

8

Test the A/C compressor clutch relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 12

9

Test the A/C compressor clutch supply voltage circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 13

10

Inspect for poor connections at 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 18

Go to Step 14

11

Inspect for poor connections at the harness connector of the HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 16

12

Inspect for poor connections at the harness connector of the powertrain control module (PCM)/engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

13

Inspect for poor connections 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 18

Go to Step 15

14

Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement .

Did you complete the replacement?

--

Go to Step 18

--

15

Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement .

Did you complete the replacement?

--

Go to Step 18

--

16

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

--

Go to Step 18

--

17

Important: Perform the programming procedure for the PCM/ECM.

Replace the PCM/ECM. Refer to one of the following procedures:

    •  Engine Control Module Replacement for the 6.6L engine
    •  Powertrain Control Module Replacement for the 8.1L engine

Did you complete the replacement?

--

Go to Step 18

--

18

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3