Did a search and found that most were having the opposite problem from mine.

I can get A/C through the vents and heat through the floor, but no air from the defroster. I had the heater core replaced a few weeks ago and am not entirely confident the shop knew what they were doing (took 'em three weeks...and he had to call in his brother who used to work at a Ford dealer to help him finish ). Any ideas?? TIA

 

There is a vacuum motor that controls the panel/defrost vents and is actuated by the blend door actuator. I found with mine that the vacuum control motor, if bad will cause the air to NOT come out the defrost vents. Apparently, the control arm can pop off the blend door arm and make it not work. I would check this first...it's a simple "feel around" process to see if it's connected. If not, check tha motor and make sure it works. If both are good, then I think the blend door actuator can cause this problem as well.

 

As a safety measure, the system should go into defrost if it loses vacuum. That being the case, find and disconnect the vacuum line. If the system doesn't go to defrost then take it back to have the people who worked on it last fix the problem. Not having defrost/defog is a big safety issue.