I'm having problems with the vents on my 2000 LS-V8. I changed the degas bottle which fixed the overheating and no heat problems. Now, even though the fan runs and I can feel the heat, no air is coming from the vents. Not even changing the settings on the climate control solves the problem. I am in northern Illinois and it is 8 degrees. I'm thinking the vent doors are stuck. Are they run on vacuum? Thanks in advance for your help.