Thermostat Not Working

Work from the simplest cause outward. If the screen is blank or dim, replace the batteries first - that clears a large share of thermostat complaints on its own. Confirm it's set to "cool" and the target is a few degrees below room temperature so it actually calls for cooling. If the display stays dead even with fresh batteries, check the AC breaker at the panel and reset it once. Then look at the condensate float switch near the indoor unit - a tripped switch from a full drain pan can cut power to the thermostat on many systems. If none of that wakes it up, the trouble is likely the wiring or the thermostat itself.

The most frequent cause is simply power - dead batteries on a battery unit, or a lost low-voltage feed on a hardwired one from a tripped breaker or condensate switch. Next is a wiring problem: the thin control wires loosen, corrode, or get nicked, and on modern smart thermostats a missing or weak C-wire causes the erratic reboots and dropped Wi-Fi people blame on the app. Third is a thermostat that has simply aged out or drifted out of calibration. Least common is bad placement - a unit in direct sun or beside a vent reading the wrong temperature - or settings changed by accident.

Florida's afternoon lightning is hard on the low-voltage side of your system. A nearby strike can surge through the control wiring and fry a thermostat or the transformer that powers it, which is why a screen that goes blank after a storm is a familiar call here. Humidity plays a part too - the same condensate backups that trip float switches will kill power to a hardwired thermostat, making a healthy AC look broken. And in the many second homes and rentals around Orlando, a smart thermostat running an aggressive schedule on a marginal C-wire tends to act up when no one is there to catch it.