Component Diagnostic Charts/Tests

Chart C-10:

Wiring Diagram For A/C Clutch Control:

CIRCUIT DESCRIPTION:

When an A/C mode is selected on the A/C control switch, ignition voltage is supplied to the A/C request circuit to the ECM. If there is sufficient system pressure, the low pressure switch will be closed and will complete the circuit to the high pressure cut-off switch and to circuits 67 and 366. When a request for A/C is sensed, the ECM will ground circuit 459 of the A/C clutch control relay. The relay will then send current to circuits 366 and 59 to engage the A/C compressor clutch. If the ECM sensed voltage from circuit 366, the cooling fan will be energized. The ECM will de-energize the A/C clutch control relay under the following conditions:

^ Coolant temperature over 255°F (124°C)
^ TPS at Wide Open Throttle (WOT)
^ Engine speed greater than 4800 RPM
^ Ignition "OFF." (Two second delay on restart)


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. The A/C compressor clutch should not engage until two seconds after engine starts.
2. See HEATING VENTILATION AND AIR CONDITIONING section.
3. A blown A/C fuse could be caused by a short to ground from the ignition switch to the compressor.

CAUTION: Not all SCAN testers are compatible with every system. A SCAN tool that produces faulty readings should NOT be used, and the problem should be reported to the tool manufacturer. Use of a faulty SCAN tool can result in improper diagnosis and unnecessary component replacement. Follow the proper instructions, located in the owners manual, for the specific SCAN tool being used.


DIAGNOSTIC AIDS:

The low pressure switch will be closed at 40-47 psi and allow the A/C clutch to operate. Below 37 psi, the low pressure switch will be open and the A/C clutch will not operate. At approximately 430 psi, the high pressure switch will open, signaling the ECM to disengage the A/C clutch. This will prevent A/C system damage.