Chrysler Pacific A/C noise
Some 2007-2008 Chrysler Pacifica models equipped with the 4.0L engine and A/C have been reported with an intermittent vibration, knock and/or rattle in the engine bay when the A/C is engaged. The issue involves loose or improperly seated compressor fasteners. The symptom may occur at any engine RPM.
Attempt to verify the condition by operating the engine through a wide RPM range with the A/C set to ON at the lowest temperature setting. If unusual noises are heard, inspect the compressor fasteners for looseness and/or small gaps between any of the 3 compressor mounts and engine mounting bosses (1-2mm). No clearance should exist between any of the compressor and engine mounting bosses.
Remove the accessory drive belt from the compressor pulley and loosen the 3 compressor mounting fasteners (2 front nuts and 1 rear bolt). While holding the compressor against the engine mounting bosses, tighten the fasteners to a value of 250 in. lbs (28 Nm) in the following order: front upper nut, front lower nut and rear bolt. Reinstall the drive belt and test. The estimated repair time is 0.5 hrs.