I live in Phx AZ and do not understand why they build 2 story houses here.
I used to live in a 2 story comdo and the upstairs was way to hot and the downstairs to cool.
The only thing I have heard about is to put in two thermostats to regulate the upstairs separately. I dont know how this works but was told about it from an air conditioner person.
I now live in a one story and only need to turn on a fan in the hotter rooms.