Air only blows out defroster vents

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...

Possible blend air door malfunction.

i believe this is a vacuum operated system. if there is a problem with the vacuum supply to the control unit, it will automatically default to defrost. i would start by checking the vacuum source lines. good luck!

the heater & defroster baffles are controlled by electic motors that open and close the baffle (doors) to let the air to the heater and defroster vents. the motor must be bad

if your ac is on max i believe it recirculates the air in the car by sucking air in by the defrost vents and blows it back out of the normal vents try to move the controls to make sure the that the shutters are working and make sure the ac is not on max by selecting the knob that has an arrow going through the little car instead of the circular one that might fix the problem

the vacuum on the rear of the engine that goes to the vacuum ball mounted n the hood may be disconnected

sounds like you have a vacuum problem

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.

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.