2001 Aurora troubles

I have a 2001 Oldsmobile Aurora with 117,000 miles on it. I have an AC problem. The AC is blowing out hot air. The first time I took it to the mechanic it was filled with freon. It got cold on the passenger side but only for about 30 minutes. The drivers side was less than that. I took it back and was told there was a leak. It was filled up with freon, then a bottle of dye to check to see where the leak was. The dye showed no leaks under the hood. The mechanic then told me that if the leak is not under the hood the only other thing was a bad condenser inside the car. This is major and I do not want to be going through an elimination process with this problem. Please Help. One more thing when the freon is put in the small unit not the large is used for the refill. Thanks