Chart C-10 A/C Clutch Control Circuit Diagnosis

Chart C-10: Part 1 Of 2:

Chart C-10: Part 2 Of 2:

Air Conditioning Circuit:

CIRCUIT DESCRIPTION
When the Heating Ventilation Air Conditioning (HVAC) panel is switched to the A/C or Defrost position and the A/C system has adequate charge, an A/C request signal is sent to the Engine Control Module (ECM). When the A/C request signal is received by the ECM, the ECM will ground relay CKT 459 long enough to adjust engine idle RPM. Once idle RPM has been adjusted, the ECM will remove the ground from relay CKT 459, which will allow voltage to be applied to the A/C compressor clutch.

TEST DESCRIPTION (Part 1 of 2)
Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM will disable the A/C clutch if engine coolant temperature is greater than 125°C (256°F). If ECM Diagnostic Trouble Code (DTC) 14 is present, refer to that chart first. Powertrain Controls - ECM/PCM

2. The A/C clutch will be inoperative if the power steering pressure switch or circuit is shorted. Refer to Chart C-1E Power Steering Pressure Switch Check. Chart C-1E Power Steering Pressure Switch (PSPS) Check

3 Refer to Diagrams/Electrical if Fuse # 20 or # 30 were open.

4. The A/C clutch will be enabled for start-up but should turn "OFF" after 10 seconds.

5. Turning the A/C "ON" & "OFF" is to check the ability of the ECM to control the A/C clutch.

6. Using a Tech 1 scanner, the A/C monitor should display "OK" because the pressure cycling and high pressure switches are normally closed.

NOTE: When the A/C clutch cycles "OFF," the Tech 1 scanner will indicate "Not OK."

7. Before replacing the HVAC control head, refer to Diagrams/Electrical for further diagnosis of the control head. Diagrams

8. Grounding the diagnostic "test" terminal at the Data Link Connector (DLC) should enable the test light.

TEST DESCRIPTION (Part 2 of 2)
9. Confirm 12 volt supply to A/C pressure cycling switch.

10. Checks for an open A/C pressure cycling switch.

DIAGNOSTIC AIDS
If the Power Steering Pressure (PSP) switch CKT 495 is grounded or the PSP switch is shorted, the A/C compressor clutch will not engage. Refer to Chart C-1E Power Steering Pressure Switch Check for power steering pressure switch diagnosis. Chart C-1E Power Steering Pressure Switch (PSPS) Check