Ford Repair: 97 Expedition Heater Blows cold, coolant levels, heater hoses

Question
QUESTION: My 1997 expedition Eddie Bauer w/ 4.6l recently began blowing cold air when set in heat mode, I have checked coolant levels and replaced t-stat, Still no workie.I have checked all fuses referenced by the OM as relating to heat and or blend door, all are fine. What am I missing?
Also when I accelerate my vents shift from dash to defrost, this I think was a condition that was present prior to the heating issue.

Thanks for your help!

Josh

ANSWER: the switching from vent to dash is vacuum related-most of the time it is a broken or rotten hose in engine compartment area

as far as cold air if both heater hoses are hot you have a blend door actuator or broken blend door problem-could be control head but not most common.

---------- FOLLOW-UP ----------

QUESTION: I will replace the actuator, but what if only one heater hose is warm/hot?

Answer
if only one hose is hot then heater core is restricted-don't replace the actuator without checking the blend door shaft they break-when you pull actuator off take mirror with light and look into actuator shaft whole and see if blend door is broke if so whole case will have to come out not a quick repair.