Should HVAC registers be closed or open when HVAC is broken, & window AC units are in use?

Question

The property in question in located in a hot climate, with high-90's being regular during the summer. The compressor has died on the property's HVAC, and for the time being, the space will be cooled by multiple window AC units and many fans, while funds are gathered for the refurbishment.

The home is a single story ranch-style, with registers in the ceiling, which lead through the un-conditioned attic space.

For the sake of maximum comfort, should the HVAC registers in each room be in the OPEN or CLOSED position?

Answer 1

They should be open, and the furnace fan should be running regularly, if not full-time. This will keep the home fresh and distribute moisture more uniformly.

If you don't run the furnace fan, it probably doesn't matter. If you find a reason to close them, do so.

Answer 2

Many homes have the air flow balanced and closing the vents will mess up that balance if it was done. Vents / dampers are not air tight so closing them may not really help and if the fan is turned on with the vents closed--it just might blow metal trunk ducts in enclosed spaces that are very difficult to repair if possible without ripping out walls. If flex ducting was used it may blow some of those lines off. I would not close the vents for these reasons.