The bill doubled and nothing feels different.
Usually the AC, occasionally the rate plan, and the AC version is often cheap to fix.
In a Phoenix summer, cooling is most of the bill. So a big jump is usually the air conditioner. Before assuming that, there are two free checks.
Rule out the non-AC causes first
The rate plan. Arizona utilities run time-of-use and demand plans where the hour you use power matters as much as the amount. If your plan changed, or your schedule changed so more load lands in peak hours, the bill moves without anything being wrong. Pull up the plan and the peak window before you blame the equipment.
The billing period. Compare days in the period and average temperatures, not just the total. A 34 day period in a hot month against a 29 day period in a mild one is not a comparison.
Something new in the house. A pool pump, a second fridge in the garage, somebody working from home all day.
Then the quiet AC causes
These do not break anything. They make the system work harder for the same cooling, every hour.
A dirty condenser coil. The most common cause by a distance. Head pressure climbs, the compressor draws more, run times stretch. Nobody notices because nothing fails. A full monsoon season of dust does this reliably.
A restricted filter. Less air per minute means longer runs for the same result.
Low refrigerant. Reduced capacity, longer runs, higher bill, and a leak that is still leaking.
Leaking or uninsulated duct in the attic. You are paying to cool a 150 degree attic. This one can be very expensive and is invisible from inside.
Fan set to ON rather than AUTO. The blower runs continuously. On a Valley system that is real money, and in monsoon season it re-evaporates water off the coil back into the house.
A contactor welded shut, so the outdoor unit never stops. The tell is a unit running when the thermostat is satisfied.
The ones that are the house, not the system
Attic insulation settled, a door seal gone, new west-facing glass, or a thermostat set three degrees lower than last year because somebody was uncomfortable.
That last one is worth checking before anything else. Each degree costs real money here.
What is worth measuring
A check-up reads amp draws on the compressor and both motors, both pressures, delta T, airflow, and the coil condition, and writes them down. That is how you tell a system working harder than it should from a system that is fine and a bill that is about the rate plan.
If it turns out to be the coil, a clean is a flat price and it pays for itself across a Valley summer more reliably than almost anything else on the list.
Questions that come with this one.
How much of a Phoenix summer bill is the AC?
In July and August, most of it. Everything else in the house is roughly constant year round, so the swing between a February bill and an August bill is very close to the cost of cooling.
Could it be my rate plan rather than the AC?
Worth ruling out first because it costs nothing. Arizona utilities run time-of-use and demand plans where when you use power matters as much as how much. A plan change, or a habit change that moved load into peak hours, can move a bill without anything being wrong.
What single thing most often causes it?
A condenser coil nobody has cleaned. It does not break anything, it just makes the compressor work harder for the same cooling, every hour, all summer. It is also one of the cheaper things on the price list.
Other things that go wrong.
The power came back and the AC did not.
Some of this is the system protecting itself. Some of it is real damage from the way the power came back.
Read itYou just got the keys.
A home inspection tells you it turned on. That is a long way from telling you what you own.
Read itYou rent, and the AC is out.
Not legal advice. A practical order of operations, and the paper trail that makes any of it work.
Read it