Econoline heater controls malfunction.

This has to do with the vacuum controlled heater ducts on the Ford Econoline Vans, If your having trouble with your heater not deciding whether it wants to be on defrost or floor, if you notice it changes when you accelerate decelerate. This is due to a vacuum leak, and most likely the vacuum reserve canister located under the heater box. Check out this video on how I repaired mine.