My sons SS will not change from defrost to vent to floor. Is this vacuum activated? It just started this problem recently. It blows some air through the defrost, but no matter where you move the knob to, there air still comes out the same. Any ideas?? Thanks

Check to see if the panel knob that adjusts the vents is cracked. It should just pull off the panel. I had a Cavalier with a similar problem. When I pulled off the knob I saw that it was broken on the inside.