I have two AC intakes on a wall , one toward the ceiling and one toward the floor. Technician said that I should close one toward the floor so that hotter ceiling air will be cooled. i've noticed that the rooms are warmer. Should I close the top one or just keep both open?
Very doubtful that either is large enough by itself.
As a test. Open both. While the A/C is running. Put a tissue at the bottom one, and see if it holds the tissue against it. Then repeat with the top one. If it holds at both of them. Then you need both of them open.
Where are your supply registers. often, the correct registers can solve warm room problems, if the A/C and duct work is large enough.