Chart C-10 A/C Clutch Control
Chart C-10:
Chart C-10 Wiring Diagram:
CIRCUIT DESCRIPTION:
When an A/C mode is selected on the A/C control switch, ignition voltage is supplied to the compressor low pressure switch. If there is sufficient A/C refrigerant charge, the low pressure switch will be closed and complete the circuit to the closed high pressure cut-off switch and to CKTs 67 and 366.
The voltage on CKT 366 to the ECM is shown by the "Scan" tool as A/C request "ON" (voltage present), "OFF" (no voltage). When a request for A/C is seen by the ECM, the ECM will ground CKT 459 of the A/C clutch control relay, the relay contact will close, and current will flow from CKT 366 to CKT 59 and engage the A/C compressor clutch. A "Scan" tool will show the grounding of CKT 459 as A/C clutch "ON."
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. The ECM will only energize the A/C relay, when the engine is running. This test will determine if the relay, or CKT 459, is faulty.
2. In order for the clutch to properly be engaged, the low pressure switch must be closed to provide 12 volts to the relay, and the high pressure switch must be closed, so the A/C request (12 volts) will be present at the ECM.
3. A short to ground in any part of the A/C request or A/C clutch control circuits could be the cause of the blown fuse.
4. With the engine idling and A/C "ON," the ECM should be grounding CKT 459, which should cause the test light to be "ON."
5. Determines of the signal is reaching the low pressure switch on CKT 66 from the A/C control panel. The signal should be present only when the A/C mode or defrost mode has been selected.
DIAGNOSTIC AIDS:
Both pressure switches are located on the high side of the A/C system. The low pressure switch will be closed at 40-47 psi and allow A/C clutch operation. Below 37 psi, the low pressure switch will be open and the A/C clutch will not operate. At about 430 psi, the high pressure switch will open to disengage the A/C clutch and prevent system damage.