We have a lot of these homes in NE Ohio using the attic as a add on bedroom
With the attic bedroom the existing system is usually unable to overcome the heat load
and the easy option is it's own a/c
They do make a/c window units for sliding/casement windows
This is just an example of a website
I have been offered a window a/c - not meant for sliders, but I can probably add a removable plywood cover on the inside of the window frame to support it. It will have to be removed in the winter and re-installed each year. It will also likely be noisy. But it is free, so I may try it.
Originally Posted by small change
Better insulation, better attic ventilation and higher blower circulation may offer e a more elegant solution But no doubt more costly!