I have new Lenox unit installed in my house in 2007 and having problem ever since. Almost every single year there is problem with the AC unit because I felted like it not produce enough cold air. The contractor guy came out and tighted the nuts and bolts and recharge the freon like 3 times already since the beginning. Now I felt like the AC is not producing cold enough air but not wanting to call the guy again because of the service fee. What can I check so I can be sure that the freon is leaked? I would appreciate all the experts' opinions. Thanks.