Bad A/C...Help?

[Panic_Attack]

So i have an 09 Altima. I bought it in October and never used the a/c until around May. It blew hot air, and never cooled down. So i took it to get looked at. They ran a leak test and a vacume test and couldnt find anything wrong, except that there was not a drop of freon in it. The put about a pound a freon in it and it ran freezing cold for about a month and a half, afterwards it stopped blowing cold again. Now i understand that 1 pound wont keep it up for long, so i refilled and charged with a LARGE can of 134a and it worked for roughly a week. Now its getting warm again. I changed the main air filter as well. So...im guessing i have a leak they didnt find, any other suggestions from more expierenced people???? :

[DJ_B_Easy]

Im not experienced, but I would check the entire system for leaks.