Floor vents let air out when control is set to OFF

I have a '98 Tahoe that I picked up a couple months ago. When I turn the air controls to OFF the air continues to flow from the floor as if I had asked for it to come out of that location. It doesn't matter where the settings are for vent control... if I turn the speed control to OFF it will always come out of the floor vents!! Ugg. I suppose this isn't a terrible problem in the summer, but in the winter I don't want air coming from there unless I ask it to. Is this a problem with these vehicles? or just mine? TIA.

Andy

I have had several GM/ Chevys over the last few years and all of them have this set up. i have never been able to identify how to stop the air from flowing through the floor vents. I can say that during parts of the year, such as summer, have the temperature knob rotated to the cooler temp settings. This should minimize the temp change from the outside.

This is called flow through ventillation. A safety feature.

DD