Have an 02 powerstroke. The heater quit working. Just put a new heater core in it a couple weeks ago. New thermostat also. The input line going to the dash is hot but there is no hot air coming out of the vents. Lost my owners manual so dont know if there may be a blown fuse or if its just the dampner or butterfly valve or some that opens the air into the vents?

 

Owners manual won't tell you anything about how to fix the heater.
I suggest going back in and make sure that you have secured the stepper motor correctly on the top of the heater assembly.
You had to remove it to get the heater core cover off.