Heater blows air thru floor vents and dash vents but no air thru defrost windshield vent

Mode Door 1.
a.This door regulates air flow to either the dash vents or defrost/floor. If you have air flowing only through the vents with no defrost or floor, this door is failing. From our experience, this door is usually the first domino to fail. Not sure why, just is.
<!--[if !supportLists]-->4.Mode Door 2.
a.When mode door 1 is set to divert air away from the vents and into the second stage of the system, door #2 chooses whether air goes to the defrost vents to the windshield or out through the floor vents in the passenger and driver's side footwells. Failure is indicated by an inability to choose between defrost and floor.
b.This door turns out to be the most difficult to replace. In order to replace the door, the dash panel has to be removed. It's still better than the dealer fix because you don't have to evacuate the AC system, drain the radiator, and remove the plenum box. But it is more work than the other fixes. When this door breaks, it falls in the down position, blocking the floor vents and diverting all air through the defrost vents. From a safety standpoint, this is good since you'd most likely rather have a clear windshield than warm feet. We suspect that a large percentage of customers will just leave this door unrepaired. You will have heat through the dash vents and to the windshield, just nothing to the floor. It's inconvenient, but you'll have to make the determination if warm feet are worth the extra work to fix the door. An extra pair of socks is easier.

Usually this is a problem with the blend doors under the dash. You either have a vac leak, a dead motor, or a faulty door.
The control opens and closes the doors to direct air thru the heater core and evaporator core along with directing air thru the vents.
When a problem occurs, the default position is the defrost vents to make sure the windshield remains clear.
You can do an internet search for "repair durango blend door" for more info.

Often a sign of a blend door problem. The blend door or doors are in the heater a/c box behind the dash.

behind the center counsel between the floor and the heater housing is a part that is called the blend door actuator. these usually go bad and have to be replaced.

sounds like bad acuator motor, this is what moves the door in heater box to set hot or cold air, and other motors to set air to blow thru defrost, vent or floor. good luck.

check for a vacuum leak in the hose going to the heater controls. Goes from engine compartment, through firewall, into dash to control head. Also, has a vacuum storage canister under hood. When system fails, it defaults to defrost.

you have a vacuum leak check the vacuum hoses behind the controll panell

your a/c and heater blow thru the defrost ( top of dash? ) and the vents. Or defrost/or the vents.? and not on the floor? Well all of these should work. can you hear the motor inside the dash turning to they're perspective spots on the dial the motor pulls a cable and closes or opens appropriate doors as the selector switch is moved. if not the switch may be faulty. and you can get it from a parts store or dealership. CK the parts store's first they will be cheaper and will be able to give you a look at what needs to be done to replace it. But it can be done on most "fine " cars in 20- 30 min with minimal hand tools.

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

Had the same problem. believe it or not i changed the gas cap and got heat all around. something about pressure.