[old_master]

If the A/C works, it means the clutch is not slipping when it's engaged. A/C clutch noise will usually stop when the clutch is engaged. The "rusty dust" may have come from the hub bearing. It's a sealed bearing, but that doesn't mean it won't wear out. Remove the serpentine belt and spin the A/C hub by hand. It should spin very freely with no noise.