Wife 2015 Chevy Traverse AC stopped blowing cold air out the other day. Took it to dealer as the AC is covered under warranty. Dealer said AC only had .2 lbs of freon and the system holds 1.7lbs of freon. They told me there are no leaks and nothing is wrong with the system so it not covered under warranty. They now want to charge me $290 for diagnostic and recharging the system. Question is if the AC is a sealed unit and nothing is wrong with it why was my freon 80% depleted