Sounds like your expansion valve is taking a shit. easiest way to find out to hook up a/c gauges to it, prssures tell you EVERYTHING in a a/c system.
also adding freon not knowing how much is in the system dosnt help anything, if your a/c was working fine, all of your shit would have frozen over, you must check your pressures, fully vacumn out the a/c system for around 15-30mins, id say 30mins our cars are old, and install new freon, but ONLY what says on the a/c sticker on the radiator support. also theres a certain amount of oil that has to be added also, its in the sticker, dont remember exactly on 240s.
BTW freon dosnt disapear in a a/c system unless its leaking, it will continue to leak until you fix it.