Start with the thermostat, then the breaker, the outdoor disconnect, the drain float switch and the filter, in that order. Each one can stop a healthy system, and checking all five takes a few minutes. Climate Pros Tucson matches you with licensed local pros when the fix is beyond a safe homeowner check.
Is the thermostat actually asking for cooling?
Confirm Cool mode, a setpoint below the room temperature and fresh batteries if the model uses them. A blank screen usually means no power or dead batteries. If you have a Honeywell, read Honeywell thermostat troubleshooting for the common wiring and battery causes.
Did a breaker trip or the power drop?
Look at the breaker panel for the AC and the air handler, since many systems have two. Monsoon season is June 15 through September 30, and the National Weather Service lists lightning, strong winds and dust storms among its hazards. A storm can trip a breaker or interrupt power. Reset a tripped breaker once. If it trips again, leave it off, because repeated trips point to an electrical fault.
Is the outdoor disconnect on?
Find the metal box near the outdoor unit and make sure the disconnect handle or pull-out is seated. A landscaper, a storm or a bump can knock it loose. Don’t open the box or touch wiring.
Could the drain float switch have shut the system off?
Yes. Many systems carry a float switch that cuts power when the condensate drain backs up. A system that runs fine, then stops with water in the drain pan, points to a clogged line. A pro clears that line. Don’t keep resetting the system around a full pan.
Is the filter choking the airflow?
A clogged filter can starve the system and cause freezing. If you find ice on the indoor coil, turn the system off and let it thaw before you call. Replace the filter on the schedule on its label.
When is it time to call a licensed pro?
Call when the breaker keeps tripping, the outdoor fan runs but the unit doesn’t cool, you smell burning, or you see damaged wiring. Those are not homeowner jobs. Check any contractor’s license at roc.az.gov; in Arizona, residential AC work falls under the ROC’s R-39 class. About 68 days a year reach 100F at Tucson International Airport, so a dead system is more than an inconvenience. The CDC advises older adults to get into an air-conditioned building in hot weather rather than rely on a fan. See AC repair and the Tucson HVAC hub, and read why an AC won’t shut off if your problem is the reverse.
When to call us
If the five checks don’t bring it back, it’s a job for a licensed pro. Ask for their diagnostic fee and whether it applies toward the repair, since each company sets its own policy. Call (520) 353-2520 and we’ll match you with a licensed local pro.