Same problem here on my '95 SE. There is a dashpot under the dash in front of the driver's right knee that pushes a lever up and down to actuate the valves in the ventilation system and route the flow of air. This lever attaches to another lever via a plastic snap ring over a ball. On my contour, this snap does not fit well over the ball and frequently pops off. If you can locate this on your car (may be different location on a '98), you should be able to fix the problem. Hope this helps!
