Best way to Trouble shoot AC

Have a 1995 Buick Lesabre Custom with 173,000 on it. Fixed alot stuff from switches to struts to plugs to filters. Have noticed that the AC is not putting out cold air. The blower is working and I hear the selector switch engage at the three different levels. I'm not sure if the compressor is activating or not and i'm not sure if the proper amount of R134a is in the system or not. Where should I look first and how? I note that Haynes repair states I should have the system discharged by a shop that can do so and not attempt this myself. Any way to do this myself if neccasary? Can I buy something at the local parts store that may assist me in trouble shooting/fixing the system? Should I just suck it up and bring it to the local repair shop and have them work on it? (I hate giving up that easy) Any suggestion would be great and thanks in advance.