I live in a 2-story rental townhome (basically an apartment with 2 stories). Our central air/heat system isn't really the best at keeping the upstairs and downstairs the same temperature whether in winter or summer.
I think this is partially because the thermostat is downstairs but also due to a not well insulated upstairs.
Winter is not as big of problem because space heaters are cheap to buy and operate. Summer is harder because portable AC units are more complicated in rental units.
We have tried closing vents downstairs but generally speaking this has not worked well.
Now that it is becoming warmer again I am hoping to find ways to determine where our unit loses its coolness upstairs to target them more directly, but am not sure how to best do this.