HVAC + Window AC question
Hey, this might be a dumb question but I can't find an answer online that explains this rather than just screaming not to close vents. I'm apologize if I'm overthinking this whole thing. I just want to understand before I 5buy yet another AC.
I am in a 3 story multi-family house with forced heating. We have an anti-Air-conditioning weirdo downstairs and above us is a massive badly insulated Attic. Our cooling in the summer has been solely Air-conditioners on our second floor. We have two window units that should be enough according to sq footage to cover the space and keep things circulating with fans but we still struggle to keep cool. We vent the attic with window fans, and insulated curtains on all windows and external doorways, but still....
My question is, would it help to cover the registers from the heating system? the system is shut down but I'm unclear if we still lose cold air through them from the heat pushing it down? It that even a thing? I'm taking an HVAC maintenance course to learn how it all works but I'm still in the basics and think I am totally missing obvious mechanics here.
If anyone can share a little knowledge or a link to a resource to explain it, I would really appreciate it.