The vent controls stopped working recently. The air only comes out of the "body facing" vents, and won't switch to either the floor or windshield defrost options. The heat and A/C work just fine, but it can't be directed to anywhere other than blowing out right in the front passenger's faces. The knob does not feel like it is loose or broken in it's socket, but there is no change when you turn the dial. I appreciate any help you can give me.