Component Diagnostic Charts/Tests

Fig. 007 CHART C-10:

Fig. 006 WIRING DIAGRAM CHART C-10:

CHART C-10

A/C CLUTCH CONTROL

FUEL INJECTION (TBI)

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 CKT to the closed high pressure cut-off switch and to CKTs 67 and 604. The voltage on CKT 604 to the ECM is shown be 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 458 and engage the A/C compressor clutch. A "Scan" tool will show the grounding, or CKT 458, as A/C clutch "ON". If voltage is seen by the ECM on CKT 67, the cooling fan will be turned on.


Test Description: These numbers refer to the circled numbers in the diagnostic chart.

1. The ECM will energize the A/C relay only while the engine is running. This test determines if the relay or CKT 458 is at fault.
2. The high and low pressure switches must be closed for the A/C request signal to be seen by the ECM.
3. A blown fuse can be caused by a short to ground in any part of the A/C request or clutch control circuit.
4. With A/C on and engine running the ECM should be grounding CKT 458 lighting the test light.
5. Determines if signal is reaching the low pressure switch on CKT 66 from the A/C control panel. The signal should be present only in the A/C or defrost mode.


Diagnostic Aids:
If the complaint was insufficient cooling the problem a non-operating cooling fan or A/C pressure fan switch. The engine cooling fan should operate with A/C on when pressure opens the switch and the ECM energizes the cooling fan relay. See CHART C-12 to diagnosis cooling fan operation.
The A/C clutch is disengaged if high power steering pressure is seen by the ECM. Also see CHART C-1E.