if you KNOW for a fact that your system doesn't have any freon (which is actually a gas) in it, then you can just loosen the lines. The chances of that are pretty slim. From my EPA class, I can tell you that it it illegal to just let a whole charge go in the air. HOWEVER, if one of the hoses was loose, or you had a slow leak (ahem), it would depressurize the system and you could go ahead and take it all out, which I assume you are trying to do.
'86 325es (TURTL3): PJ peetsa hawler
'87 535is (BADWATER): almost done... really.
'86 325e (GRN HLL): DD/show/rocket
'04 x3 3.0i: Wife's Bimmer (manual, woot!) My BMW Blog