In the Phoenix metro, cooling is commonly half or more of a summer electric bill. The good news is that the biggest wins are cheap or free, and the expensive ones are easy to rank once you know what the cheap ones are worth.
Free: stop fighting the peak
Most Valley utilities bill on time-of-use or demand plans with expensive afternoon windows. Pre-cooling the house a couple of degrees before the peak window starts, then letting it drift up during it, shifts real money without making the house uncomfortable.
Check which rate plan you're on before doing anything else — a lot of households are on the wrong one for their schedule.
Cheap: filters, thermostat behavior and shading
A loaded filter makes the blower work harder and drops your airflow, which drops capacity right when you need it. In a dusty part of the Valley, check monthly instead of following the box.
Close blinds on west-facing glass before mid-afternoon, not after. Once the sun has been on that glass for an hour, you're removing heat that's already inside.
Run ceiling fans only in rooms people are in — a fan cools skin, not air, so an empty room with a fan running is just a small heater.
Worth paying for: coil cleaning and a verified charge
A dirty condenser coil can add 20 to 30 percent to run time. A charge that's 10 percent low quietly costs capacity all summer. Both are routine maintenance items, and both pay for themselves in a single Valley summer.
Worth paying for: duct leaks in a hot attic
Arizona attics run 140 degrees and up. Ducts leaking 20 percent up there aren't just losing air, they're dumping your cooling into the worst place in the house and pulling superheated attic air back into the returns. Sealing returns and plenums often does more for comfort than upsizing equipment would.
Usually not worth it first
Replacing a working 12-year-old system purely for efficiency rarely pays back before the new unit is halfway through its own life. Fix the airflow, the charge, the coil and the ducts first, then reassess. If the system fails anyway, you'll be making the replacement decision with better information.