1995 Buick Lesabre climate control not working right...hot air coming through vents..
 

I'm having trouble with the heating/ac system in my 95 buick lesabre. Hot air is coming out of the vents even though the I have the selector arm all the way in the cold position in the climate control settings. The only way to get the hot air from leaking from the vents is moving(sliding) the climate control lever from hot to cold back and forth, exercising the control by mving the lever over and over again. Than I can get the ac to shoot cold air. Anyone know why this is happening and how I can fix it? Thanks