I replaced the heater core in my 2002 F-150 5.4 4x4 myself a couple weeks ago. In Colorado so outside temp is cold. I trun the dash to cold and only hot air blows. Inspected blend door while I had it out, nothing looked bad. Didn't do this before. I am wondering if I could have missed a connection for the blend door actuator or??? The blend door was in the position that puts it against the heater core when I got to it. I don't know if that is open or closed, hot or cold. I hope I don't have to take the dash apart again... But if I do, I do.