No air flow out of one vent
I have no air coming out of one of the vent. I had my entire duct professionally cleaned and the duct cleaning guy confirmed there is no blockage. He advised to close all the vents in the house but this vent. and Now I have air flow in that vent. But as soon as I open few other vents, there is no air flow. I have attached a picture for your reference to show how this vent branch is connected to trunk. Please suggest what is wrong with the design and how to fix this? This vent never worked with other vents open.