Idle Speed Stabilization (A/C Compressor Engaged)

Set parking brake. Run engine at idle and warm up to operating temperature. Engine should idle between 670-770 RPM. If correct, test is complete. If not correct, go to next step.
Using multimeter, test input voltage at ECU between terminal No. 19 and ground. Readings should be 12 volts with A/C compressor on and zero volts with A/C compressor off. If reading is incorrect on either test, repair short in circuit. If reading is correct, test is complete.