Ac problem

I have a 1994 roadmaser wagon with close to 160k miles on it. I have been having a problem with the ac and heat they both work but not very well. On a hot day in the summer the ac wouldn't get cold enough to do anything. The heat works slightly better but not much. When I turn them both of I hear a hissing sound that doesn't stop. Any ideas to what the problem could be.
Any help would be appriciated.