1995 Buick Lesabre vent function not working in heat or cool.....
 

I have a 1995 buick lesabre. My heat control is acting strange. My heat works fine however if my control lever is turned to cold hot air comes out of the vents. The only way for me to get the heat from coming through the vents is to move the lever back and forth from warm and cool until the heat stops coming out.
My question is... is this problem a failed door actuator or the heat control? This setup is NOT the digital dual heat control. Any suggestions would be great. Thanks