Customer has very little air flow in master bedroom close to none, said problem has been like this for awhile, they are trying to sell home, found damper slightly open for supply run also supply run for master bedroom is longest in the house, customer has a electronics air filter on system and suggested putting a thinner filter in unit due to furnace being belt driven and needs as much air as possible, also suggested duct cleaning as well hasn’t been done in years could remedy the situation, you can’t see full length of supply runs they go through the walls so it’s possible something has come detached. Customer will try filter first and see if that works