I own a three story townhouse. The central AC unit is on the bottom floor, but there is one particular room at the top level where the air flow is very weak. This contributes the room being very hot in the summer time, and very cold in winter months. I was told by my home-warranty program that I should have the ducts cleaned out for maintenance purposes, which I did, but it's barely noticeable, in terms of increasing the air flow to that room. The AC works fine in the rest of the house. I was told it could be fixed by redirecting the air flow in the "dampers". Do you have any other suggestions or ideas as to what could be causing this, and how to address it?

Is there another unit identical to yours? If yes you might want to talk with the owners to see if they have same issue. It sounds like the ducting was kinked during the install or a child may have droped a toy down the duct after removing the register.