Weird Central Air problem

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I have a weird problem (at least it's weird in my opinion) issue with central air.  In a 2 story townhouse, the air doesn't seem to be getting up to the 2nd floor.  I had a new HVAC installed a few years ago and it didn't fix the problem.  There are some vents that you can open/close that lead to upstairs and I opened and closed them a few times -- didn't make a difference.  The people that installed my HVAC said that it's how the townhouse was built and the air just doesn't get all the way up there cause all of it comes out downstairs....just can't believe that this is true but not sure what else could cause it.  Any ideas??