Air Conditioning (A/C) Compressor Clutch
WARNING: This page is about a different car, the 2013 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
When battery voltage is applied to the A/C compressor clutch field coil, the magnetic force locks the clutch plate and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate.