A/C blows cold only through the floor and defrost vents

Hello,

It sounds like you have a faulty mode door actuator.
The mode door actuator is what controls where the air will blow from. Many times, this component fails by being stuck at any one of the positions and won't allow you to change it.
The mode actuator is located on the HVAC box behind the dashboard. It will require removal of the lower part of the dash to access it.

Here is a helpful guide:

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

I have attached diagrams below for your reference.

Let me know of any questions.
Thank you.