Ford Repair: heating system in 99 ford Windstar, dual heat, ford windstar

Question
I have a 99 Windstar with dual heat and air.The front heater part is not getting cold ,the back is.There is A WHITE BOX UNDER THE DASH THAT IS CLICKING.its got a square plastic rod that runs to it that acts like its hanging or slipping makeing a noise.What is this little box?Is it a switch and about what does the item cost.Does the dash have to come out to replace this if its causeing the problem?  

Answer
The little white box is a Blend Door Actuator.  If it is bad, you should be able to remove it and reinstall a new one.  If the blend door that it is operating is stuck or broken, you might have to remove the dash to replace the door.  It is more common for an actuator to go bad then a blend door.  Replacing the actuator would cost around $200-$250, replacing a blend door would cost around $700-$900.

I hope this helps,
Dave