My A/C is not putting out the cold air the way it used to. The air is chilly, but not cold, anymore. It gets colder when the RPMs are higher, and not as cold at idle. I checked the pressure on the low side, and it seems to be just fine. It has been about 5 years since the system was filled. Is it possible that the freon is bad, or is it possible that the problem is something worse?