I also have the problem of no heat for passengers. Took TC to my dealer in November. They had it for a week trying to take care of the issue. The mechanic was back and forth with theFord engineers and did not get any satisfactory information. They also had another new one on the lot and he said it was the same. Air but very little to no heat.
I do know that because these heaters are independant electrical units (the frontone works perffectly) it has nothing to do with the engine coolant, temperature, etc. It is like you have baseboard heat in the car. But why does the front work and not the back?
Ford engineering needs to deal with and correct this problem now. Otherwise I am very satisfied with this vehicle.