I have a 2000 STS, that began to blow warm A/C about 6 months ago. First it was on blowing warmer on the driver side then on the passenger side. It was also blowing noticably cooler when i was stopped at idle, then when i was driving with the rpm's up. eventually the a/c started blowing warm on both sides. i checked the refrigerant level and it shows that it is normal, and the system doesn't appear to be leaking. I had a friend tell me it sounded like a vacuum leak in the temp. control system that is not pulling a vent door closed. Does this make sense? If the environmental control system is run on a vacuum system, where would i check to see if there is a vacuum leak?