New homeowner of a 1944 house here. My AC is assaulting some of my house and is barely leaking out of the vents in other rooms. Particularly one bedroom is not getting any cooling. I took off the vent and can't feel any obstructions.
I found some strange levers on the ceiling in my basement on the ducts that come from the boiler unit and they are turned all which ways:
I tried having someone stand near various vents and turning them all which ways, but she couldn't really tell an effect for most of them. The one labeled MBR definitely controls the master bedroom and when I turn it the airflow drops out of the bedroom, but it doesn't show up in the other two bedrooms.
What direction should these levers be in? Is it "closed or not closed" or is it finer grained than that? How can I deterministically tell what these do?