Double check that.

We added AC to our new house a couple of years ago. Our house is newish, only about 8-10 years old at this point. The AC installation itself was fine. But the ducts that run to the upstairs are woefully inadequate in terms of size and airflow, and the single return-air vent in the hallway doesn't suck enough air through to make it worthwhile.

As a result our upstairs is about 5-10 degrees warmer than the downstairs during the summer, it'd be even worse if I wasn't doing a bunch of mitigation: I close some of the downstairs vents to get more air upstairs, but you can't do too much of that without causing excessive static pressure, which is bad for the fan and compressor. Without any return-air vents in the upstairs rooms, we have to keep the doors to all the bedrooms open at all times except when sleeping, in order to keep the air flowing. I have to program the system to run the fan 75% of the time, to keep the air circulating even when the cooler isn't on.

At least the AC held up during the heat wave last weekend. During that, my band went to our cellist's house on Saturday to video us playing an outdoor concert; it was over 100 in Redmond. Crazy stuff, but she had AC too, so we got to take breaks in the cool. That was some work, though.