Our 99 S-10 Blazer is an LT with automatic AC controls. The Blazer just turned 80K. This problem has gone on for now for about 2 years. I have replaced the control until in the dash and the blend door actuator. I also trained the controller and actuator by pulling the fuse then reinstalling it worked great. This spring a new compressor and kit were installed due to oil leaks at the compressor. When we start and go for any where from 10-15 minutes or maybe a few hours everything works great. Then with the compressor still fully engaged we get a louder than normal fan roar, from behind the glove box, and little to no air out the dash or lower vents. I have also replaced some of the accessible vacuum lines and the check valve. How is the vacuum reservoir accessed?? And do they fail could this be the problem???