A/C blows hot at times

The A/C in my vehicle blew hot, humid air whenever I turned it on and would not cool down until I drove over 20mph for a few minutes. In other words, if I was rolling down a street or idling, it would not cool off. It was very noticeable as I would be driving with hot air blowing, and then all of a sudden, it would start blowing cold air. Also, if I ever had to punch the accelerator, it would kick off the A/C and blow the hot, humid air that I was used to at start up. I live in Florida and, needless to say, this was abnormal. At about 60,000 miles, I reported it to the dealership. I was told the A/C mechanism was small and that it would take some time to cool the vehicle down. However, it wasn't that I wanted the car to cool down quickly, I simply wanted the vehicle to begin blowing cold air moments after start up instead of hot, humid air. At 90,000 miles, I reported it again. The vehicle was looked at by the dealership and they said it's low on freon. They suspect a leak, so the vehicle has dye in the A/C lines to see if it will blow hot again and find out what's going on.