Sounds like that is the problem. Bad clutch assembly on the compressor or something internal jammed. If would fix that ASAP or you may strand yourself on the side of the road.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.