My grandmother has lived in the greater Phoenix area for about 20 years. I went out there every single summer from about '86 to 1998. It is some of the most beautiful weather this country has to offer as far as the rest of the year; and the summer is bearable (hence, my return year after year). I actually, just got back from my trip out there the tail end of July; the hottest day was 118, but like I said it's bearable and when it's not go inside. Everywhere that's worth going has an A/C; if the place doesn't have an A/C stop going, even if it's your cousins house.

You will definitely fall in love with early evening and even late night swimming; it doesn't get much cooler than about 85 at night. I would tint my windows, and get sunshades for your car (ESPECIALLY IF IT'S LEATHER LIKE MINE); my car was 159 inside the day it hit 118, now that will hurt your baby, so NEVER LEAVE HIM/HER in the car! Again though, a lot of places have covered parking so that may not be too much of an issue.
As far as your housing, have you already found a place? When I was out there I was negotiating a deal with a developer and got some pretty good pricing for my investors. No downpayment, no closing costs, and all that other good stuff; so let me know if you are still looking for a place. They have a few developments going (Chandler, Tempe, Scottsdale, and some other place that I can't pronounce let alone spell, something-tukie i think).