Cadillac: 88 Fleetwood FWD Air Conditioning, r 12 freon, 12oz cans

Question
Went to charge my A/C today and actually put 3 12oz cans of Freon in and cold air was coming through....suddenly LOUD hisses and sputters came from the engine and from what I could tell in the area of the Compressor(?).  Have you seen or heard of this?  What can I do?  Do you know where I can get info on the layout of the A/C system on this vehicle?  We bought this car a few months ago and the individual failed to tell me that it wasnt working....or did I fail to ask him...hehe!.
Anyway, what can I do or what do I need to look at, etc...  
Is this better off in the hands of an A/C mechanic?  I hope that I can do something on my own first to avoid heavy costs....

Thanks!
Ken

Answer
Either you put to much freon in the system and the safety blow-off valve dispersed the overcharge.

1. Evacuate the system using a vacuum pump and a set of AC gages to 28" of vacuum and make sure that it holds this amount of vacuum on the AC gag and then install the correct amount of R-12 freon.