Anyone balanced their AC system? I have a two story house and the downstairs gets ice cold and the upstairs stays hot. Someone mentioned I should install dampers? Why would the house have these pre-installed?

So I'm a little confused. Hoping someone can offer some advice.

I have a 2500 sq ft house, two floors. It has a single AC unit for the entire house.

The issue is during the hot months, with the thermostat being downstairs, it cools the downstairs to say 72 but the upstairs is like 78+.

I bought some remote sensors for my thermostat so I can tell it to cool based off the upstairs temp.

However now, when my upstairs sensor hits 72, my downstairs is like 65 and freezing.

I mentioned this to a friend and he said I should check for dampers in the attic – I can't see anything on the ducting so I have to assume I do not have any.

Is it an expensive project to get these installed and my AC balanced?

Why wouldnt the home builders include this in the AC plans. Seems really short sighted not to be able to control your air flow to multiple floors.

The only thing I can see is that the vents on the ceiling have tabs that I can pull closed, but I've been told that closing those or restricting the flow is harmful to your AC unit.

It's really annoying because I have to either freeze downstairs, or sweat up stairs depending on which sensor I set my AC to.