Hissing Air Conditioner

I have a 97 Buick Riviera 3.8sc with about 133k on it that just today started making a hissing noise from under and inside the dash. Its worse when turning left or jumping on the breaks. When I turn the air off, the hissing stops. Is there air in the lines, or a clogged valve or something? It kind of sounds like its boiling against the inside of the lines. Is this something I could fix or do I need to take it to a mechanic. Thanks for the help!