Heater A/C blend door

I have a 03 sable 52000 mi. 24 valve. Has automatic climate control. It worked fine tilll 3 wks. Ago. The a/c is charged and lines cool under the hood, but no cold air in car. Also no hot air at the floor when heater is on But heat at the upper vents is good. Ford dealer said the blend door was warped. They replaced the door. It worked for a 3 days, and did the same thing, I took it back to them, they worked on it 3 hours or so and said foam got behind door. It worked ok for a few days and now no a/c or heat at the floor again. I can see a lever moving at the heater case under the dash when I push in the buttons for lower heat. What can I do to fix, Is this a problem with these cars? SABLEGUY :x