Got an '84 F-150 with the 300 I-6, it is equipped with the FX-6 (I think) compressor. When I have the air on, a whine comes from the compressor that matches the engine speed (sounds kind of like a power steering pump on it's way out), with the air off, the clutch tends to rattle. I am getting really cold air out of the vents, seems to work just fine.

Whats the deal??

 

It may be the sound of the compressor on the way out.

You may want to throw a couple ounces of system compatable refrigeration oil in there and see if that helps, either way it won't hurt it.

Off top of my head I'm not sure if FX 6's black death unit or not.
Check around & find out for sure. If it is, you don't want it failing in your system. That fills system with carbon particles/ shards when it beaks apart internally, thus name black death . . . .

In either case you may want to consider getting a rebuilt or new compressor this winter when A/C work is "off season", if you determine it is a black death unit. FBp