Hmmm, Where are you located? How old is the house? Is the bed room facing South other than furthest from a/c unit. IMO, you have an oversized unit for the size of house. BToo big a unit is nno good for optimal effciency. Idea of bigger is better in a/c unit is wrong.
OMG, we have a winner ;-)
Yes, a 5-ton unit feeding only seven 6 in. ducts with the dinky little registers would make no sense. While stupider things have happened, I very much doubt that's the OP's configuration.
The OP certainly does need to inspect his ducts carefully and should be building some understanding of how much air is being moved where while also looking for leaks and other problems.
Are ducts insulated, I did mine and it made a big difference. Have you tried running the fan continously, I do that on hot days and nights it makes maybe a 3f difference in balancing it over 24 hours. Do you have any vent dampers on the air handler-furnace. I put them in to get a more balanced heat and AC, but be carefull you dont want to cut air much to other rooms or you risk freezing the coil. On one long weak run I had a bigger insulated duct and a larger vent to reduce resistance and get more airflow. A window AC would do it today to get you cooler, but there maybe several small jobs that could balance you out fairly closly, just the fan on continously and a small adjustment to floor registers might help alot. Everyone saying 7 isnt enough isnt true, size is what matters not the number of them, if it wasnt enough for airflow you would have frozen the coil and had no AC many times before, till you thawed it out. Insulating can be easy to do for two people, vent dampers are easy to install Diy. While you are at it if you cant examine the interior AC coil cut in a hole in the ducts and make a cover so you can look at it, it needs to be clean and mold free or performance suffers and electrical costs can go way up. To cut a hole you must know exactly where the coil is so you dont ruin it. Is this house in a hot unshaded area, because that is a very large AC for your sq ft, does it cycle alot on the hottest days or run near continously, it should run continously if its not oversized on the hottest days to remove the most humidity, an oversized AC wont run long enough to cool the farthest run so running the fan continuosly might be needed and worth a try .
Thank you. I'll also point out, as did someone else, return air circulation is critical also. If you don't have a return and close the bedroom door, you won't get air in.
FYI Dave (ilbebauck's real name) is a HVAC hack. Just ask any of the real techs in alt.hvac what they think about him and his "advice" Be sure to mention daveinlakevilla and daveinillinois, nics he was using there untill he was chased off
Even here in Alabamastan, a well insulated 2 story home can be cooled by a 2 ton AC unit, it's all about heat load. I have one customer who has a new home and the upstairs heat pump is larger than the downstairs unit, why? Because the upstairs has some very large windows that reach all the way to some very high ceilings.
TDD
In a residential application, you are limited by how big the supply registers/boots are especially if the ducts are run down a stud space ..therefore, the quantify of ducts IS important in such instances. If the ducts are ran in the attic into the second floor ceiling with the airhandler located in the attic too, then you have much more leeway on the size of ducts , etc.. His best bet is to get a professional out to his house to look it all over , as those of us replying here cant see the entire installation from our laptops...and can only offer up some vital considerations in a general sense.
It still goes back to the size. If you have ten ducts of the wrong size, cooling is is not as good as five of the correct size. Sure, you may need two if the space for one is too small, but no matter the number, the size is the overriding concern.
Agree, if simple steps don't fix it
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