First of all. I would think that your time to sue has long expired, the warranty is up. Another funny thing about lawsuits is that you will sue the guy, his insurance company will then take over. They have a lot more money and time than you do. Probably a few attorney's on staff. They will draw it out and paperwork you to death, while you are paying a fee to your attorney. Let's say in 2-3 years you finally get to a trial and you win. Now they appeal it. You're still paying your attorney for the mounds of paperwork you will get. 2-3 years later it gets settled and you may or may not win, if you're not broke by now. Probably even moved. My advice is to have them figure out why the compressor goes out. If under warranty still from manufacturer, then pay to fix it and fix the problem. Modify the ductwork to accomodate the tonnage and balance the system for your comfort. 1/2 ton larger really isn't that big of a deal honestly. It's very minor. If they put a 5 ton on when you needed a 3 1/2, that is pretty good jump. But 3 to a 2 1/2 isn't much at this point.