Fix Heat Door Actuator.
This will work on most cars.
Blend Door? Or ... ?
Here is a video to help solve a real problem: The Heating and A/C controls would not work. The air would only come out the Defrost Vent. Here is the simple solution I found to solve this problem for free. Normally for such a problem as this, you would change the Blend Door Actuator module, however as you will see, you can first check your dash switches to see that they are plugged in. Here is how you do it ...
Simple how to fix blend door heater a/c actuator 2002 - 2008 ford explorer noise behind dashboard
This video shows a quick fix to get you thru the winter (with heat) if your blend door actuator is not working. I put a zip tie around the latch and route it thru the dashboard so I can just reach over and pull it to close the blend door.
Where is it and What's it look like
On a Lincoln and some Merc Grand Marquis the heat and ventilation system is very difficult to get to and test. The actuators for the vent and defrost doors are absolutely impossible to see or access without removing the dash panel. Here is what you are looking for.