Hi all. I just bought an older home. It had a new master bedroom added in the mid 90's. The original house stays cold, but the master doesn't get cold at all. I checked the planum?? In the attic, and the duct is attached and not leaking air. Because of the way the roof was installed over the addition, I can't follow the duct all the way to the vents. How would I check to see if the duct is pinched or obstructed? Any suggestions would be really helpful. I'm in Louisiana and it's hot and muggy even at night.

Sounds like this add-on room is drawing from the very end of the supply ducts. Many people add on a home and assume their furnace can handle the extra space only to be disappointed. This may be your case. If there ius a return in the bedroom make sure its open and partially close the returns in other parts of the house. Also try partially closing the supply registers in the lowest level to help boost the amount of air reaching the bedroom. You can also add a duct boost fan.

Thanks you for your answer. I only have one return in the house and that's in the door where the inside unit is. Do I need to install a return in the MB? The house is only 1492 hsqf. The duct that runs to the MB is probably the longest duct. Is it difficult to wire in a booster fan?

Duct boostera aren't too difficult. The manufacturers know DIY folks will install so they give great instructions. Getting the 110 vac is usually the hard part.