Was coming back from a football game on the interstate Saturday and noticed my ac was not cooling very well. When I came off the interstate it started cooling better. The next morning when I cranked the engine, I heard a whirling sound. Think it might be my air conditioning compressor. I have a 4.2 1999 F50. The center wheel on the compressor{ clutch} turns when I turn on the air. When I turn it off, it stops and actually turns a litlle the other way? Any ideas