brian0918 wrote:
We have central air, and the upstairs stays around 85+ (in 100%
humidity) despite the temperature downstairs staying at 75 or less
(ie, whatever the thermostat is set at). IThe upstairs has two
fully-open vents through which little air blows, and what appear to
be 2-3 vents for the warm air to exit. Can anything be done to help
cool the upstairs? The curtains/blinds are kept closed, and the door
leading to the upstairs is kept shut to prevent any warm air
downstairs from moving upstairs.

Also, attached to our air conditioning system in the basement is an
air cleaner that doesn't work, and when you remove the cover from
that, a ton of air is pulled in. I've noticed that this causes a lot
more cold air to be forced through the vents, substantially cooling
the upstairs. However, we asked someone who would know about these
things, and he said you shouldn't do that (for some reason). Any
information?

We can't tell from here, but it may be a specific problem like the air
cleaner or dirty coils preventing air flow or it may be a bad or damaged
duct design. You will need a local pro to check it. Ask around and find a
HVAC professional that is recommended and have them check it out.

--
Joseph Meehan

Dia duit