Remove your ducted AC and look inside the 'hole' in the roof. We had a problem with our Voltage. Whoever metal taped the interior of the hole failed to vacuum out the sawdust. What happened is the metal tape rolled itself up into a ball and much of the air was lost into the ceiling rather than going through the ducts. I removed all the tape, cleaned out the hole, and re-taped. It mad a decided increase in the airflow. Another item was the two intake vents in the ceiling. The openings were closing down and I put a piece of PVC pipe in there to hold the intake open. Now the ducted AC moves a lot of air.
