You can fix this
Likely cause: a float switch cut the power
Water backing up in the drain pan can trip a float switch that shuts off the system and the thermostat with it. Clear the drain and power should return.
Why this happens
Honeywell lists an engaged float switch among the causes of a blank thermostat. The switch sits in or near the drain pan and cuts power when water backs up, so the pan doesn't overflow. A clogged condensate drain line is the usual reason.
How to fix it
- Switch off power to the indoor unit.
- Soak up standing water with towels or a wet/dry vac.
- Clear the drain line with the vacuum and vinegar steps in the AC leaking water troubleshooter.
- Restore power. The float switch should reset as the water goes down, and the thermostat should come back on.
If this does not fix it, tell the HVAC technician
- That you found water in the pan and the thermostat was blank.
- How you cleared the drain and whether it has clogged before.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
References (every fact above comes from one of these pages)
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