HOT AC on 1998 Cavalier

Posted on another thread but thought maybe I should start a new one on this problem. My dad has a 98 cav. Keeps losing Freon. Has had it charged 3-4 times and dye added same. He watched them last time to make sure thery added it. Can't find the leak. Only takes a day to lose the Freon. They add about 1 lb of freon each time. Runs nice and cold for a day or so Then HOT again.

They talked my dad into replacing the evaporator which is located way up under the dash. didn't solve anything.
Any Ideas out there?