Usually when the compressor goes south it will make some nasty sounds, at least thats what mine did. Depending on the condition of the compressor you may be able to rebuild it, that would be the cheapest fix. Otherwise a remained compressor i believe is between 300-400 dollars, not 100 percent sure. If the 4.9 has the same location as the northstar it is a bitch to change out. Its on the bottom of the engine, which means the engine will have to be dropped to access it, better left to a mechanic, in my opinion.