Check these in order
- Dead batteries. Many thermostats run on AA/AAA batteries. Pop the faceplate off and replace them — the most common fix.
- Tripped breaker. Check the panel for the air-handler and AC breakers; reset any that are tripped.
- The float / drain safety switch (the Florida one). If your condensate drain clogs, a safety switch cuts power to the system — and on some setups the thermostat goes dark. Clear the drain line and empty the pan.
- Blown low-voltage fuse. The air handler's control board often has a small 3–5 amp fuse that blows and kills the thermostat. It's a cheap part.
- Loose or chewed wiring / bad transformer. If power isn't reaching the thermostat, the 24V transformer or a wire may have failed.
What repairs cost
| Fix | Typical Florida range |
|---|
| Batteries (DIY) | $5–$15 |
| Clear clogged drain (pro) | $75–$250 |
| Low-voltage fuse | $75–$150 |
| Thermostat replacement | $100–$350 |
| Transformer | $150–$350 |
If batteries and the breaker don't fix it, a clogged drain tripping the safety switch is the #1 Florida cause — check that before assuming the worst.
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Handy parts to keep around
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Smart thermostat
If yours is failing, upgrade and save on cooling too.
View on Amazon →Drain-line tablets
Prevent the clog that trips the safety switch.
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