Do this, buy a can of Dupont Suva WITH DIE ($8 at Autozone) and a incandescent black light from Wal-Mart for less than $20. Add the Suva with Die (adding the Suva with die will add a UV die, kinda like highlighter liquid, and will cause the leak to show up, especially under a black light), run the A/C at night and scan both inside the car and within the engine bay with the black light for bright ass A/C leaks. If you do not see any bright ass drips, sprays, etc. after I'd say, 2 or 3 hours of letting it run, then sit, then run, more than likely you do not have any leaks. Personally, that would be my next step as it will prove whether or not there are any leaks. Remember, always diagnose then repair!! Shoot-from-the-hip maintenance (a.k.a. replacing things at random) or people telling you what is wrong without proof is not the game you should play with your car, especially if you want your moneys worth! Just because this "Certified Mechanic" said it's good, have him prove it or prove it to yourself by diagnoses. Remember, test/diagnose then repair, do not repair then repair again when that doesn't work!