Air only blowing on defroster and floor not through the regular vents I change the actuator not difference

Question edited for clarity and toss in some upper CASE letters.

There are all in one place under the centre of the dash.

https://www.google.com/search?q=2013+Lincoln+MKS.+Mode+control+actuator+location

This sounds like an actuator. There is usually several (three or four) on different vehicles. There will be at least one that directs the air to different locations such as defrost. You also may have a defective selector switch. I would check this before I changed the actuator or blend door. If the blend door is defective, this usually calls for totally removing the entire dash panel and usually requires several hours work. If you have to have a repair shop do this it can be very expensive.

A vent flap actuator probably needs to be replaced. It's what moves your vent flaps from heat to A/C or to plain "vent air" when you change settings.

The discussion in the link includes vent flap actuators. Unfortunately, they also include the infamous no low speed fan problem too.

Cannot get any air from dash vents while defrost and floor vents work fine...

Your particular actuator will be a different one than they found.
They're all a absolute pain to get at because they can be well buried in the dash. I would start looking under the dash on the passenger side, that's where most of the air control is. Cannot get any air from dash vents while defrost and floor vents work fine...

Which vents, floor--defrost--dash? Can you hear the blower motor running? The squirrel cage could have broken loose from blower motor? There could be an actuator problem under the dash? If actuators are vacuum controlled and vacuum is lost, it might default to defrost, only blow out defrost vents.

Not sure what year, make or model vehicle is in question, but the issue is due to an actuator that has gone bad. Sometimes referred to as a mode actuator or blend door actuator. This actuator controls where air/heat will blow from (defroster vent, forward vents, floor vents or combo, etc.). Good luck. Ron @ Speed-O-Repair.

Possibly some blockage? Foam where it shouldnt be?

There is no vacuum to the controls. Look for a vacuum hose that is no longer connected to the engine intake manifold and repair it.

If you are referring to the air won't blow through the defrost vents or on the floor, you may have a stuck or broken blend door actuator. This part diverts air through the different settings: defrost, vent, floor etc. If you aren't getting warm or hot air regardless of the settings, you may either be low on coolant or have a bad thermostat.

Sounds like a faulty blend door actuator. This part diverts air from the different ports ie floor, vents, defrost. If it keeps changing when you hit a bump, either the actuator has a loose connection or it's bad all together.

Removal & Installation

1. Remove the floor air outlet duct extension from the floor duct.
   
2. Remove the center console, if equipped.
   
3. Remove the screws from the center console duct, if equipped.
   
4. Remove the center console duct, if equipped.
   
5. Disconnect the electrical connection at the mode actuator.
   
6. Remove the mode actuator mounting screws from the HVAC module.
   
7. Remove the mode actuator as an assembly with the actuator cam.
   

Mode actuator location

To install:

1. Install the mode actuator as an assembly with the actuator cam.
   
2. Line up the heater/defroster valve lever with the mode actuator cam slot.
   
3. Line up the A/C valve lever with the mode actuator cam.
   
4. Install the mode actuator mounting screw to the HVAC module and tighten to 14 inch lbs. (1.6 Nm).
   
5. Connect the electrical connection at the mode actuator.
   
6. Install the center console duct, if equipped.
   
7. Install the screws to the center console duct, if equipped, and tighten to 14 inch lbs. (1.6 Nm).
   
8. Install the center console, if equipped.
   
9. Install the floor air outlet duct extension to the floor air duct.
   
10. Calibrate the HVAC module actuators.