A system in the Valley runs close to nine months a year. That's roughly triple the seasonal duty a unit in a milder climate sees, and it means the small stuff catches up with you faster here.
Start with the filter. A clogged filter starves airflow, ices the coil, and eventually trips the system off entirely. In a house with pets or a dusty street, monthly is not excessive. Then look at the outdoor unit: clear at least two feet on all sides, cut back anything growing into it, and rinse the coil fins gently from the inside out with a hose, never a pressure washer.
Find the condensate drain line and confirm it's actually draining. A clogged line is the single most common reason a working system shuts itself off in August, and on a system with a safety float switch it will do exactly that, usually on the hottest day of the year. If you have a secondary drain pan and you ever see water in it, that's your warning.
Check the vents. Every supply register open, nothing blocked by furniture, and return grilles clear. Closing vents in unused rooms does not save money on a central system; it raises static pressure and makes the blower work harder.
Then there's the part you can't do from the ground: refrigerant charge, capacitor and contactor condition, blower amp draw, temperature split across the coil, and static pressure. Those readings are what a maintenance visit is actually for. A capacitor that's drifted out of spec costs very little to replace in March and takes the compressor with it in July.
If you're due, we're currently running 15% off your next maintenance service. Booking it before the first hot week is worth more than booking it after.