My AC makes a loud noise when cycling. Also it never gets any cooler than 75. Could this be my compressor? How hard is this to fix yourself?

If the noise is a screech coming from the furnace, it is a dry bearing in the blower. You might be able to oil it or replace it.

If it is a loud engine type noise outside at the compressor, there is little you can do. Chances are, you will need to replace the compressor. To do that, you must pump out any Freon left, cut the lines and silver solder the new lines. Then you must add the proper amount of Freon. You must have a license to buy Freon. As you can guess, I am saying you can't do it.

I do as much of my own work as I can. When I replaced my airconditioner a few years ago, I set the compomnents, and ran the tubing, but paid a professional to do the soldering, filling, and adjustments.