I have a 1994 oldsmobile 98 regency and the air comes out of the defrost vents only.?

I can switch the controller on the dash and the light on the switch changes position but the air only comes out of the defrost. If the control head is electronic push-on how can I troubleshoot this problem and what all could be the problem? The controls on the dash are ons, electric ones. There is no stitch to move or anything like that. I just push a on and the led light in the switch comes on but air flow does not change from defrost.