I am about to have my a/c replaced. The existing system doesn't work too well. On a 95 degree day the living area is 7 degrees hotter than the back of the house. My contractor wants to move the air handler (in the attic) from its central location to above the car port. This will make the supply plenum length about 70 feet long, and will require rebuilding about half of the supply and all of the return plenums. I am concerned that this great length will rob air to the bedrooms located at the end of the run. My contractor says this won't happen, but I have doubts. For $7+Grand, I want the job done right. I was thinking about just adding a damper to force more air to the living area. In this way I can keep the existing system and maybe save some $$.
Could someone please advise me if my contractor's proposal will work o.k.? I have attached a .pdf file showing the a/c layout.