You can fix this
Likely cause: the thermostat has no power
A blank thermostat can't tell the AC to start. Dead batteries are the easiest fix, so start there.
Why this happens
Trane lists dead thermostat batteries first among the reasons an AC won't turn on. Honeywell's support page adds that the system itself may have lost power from a tripped breaker, the furnace door safety switch, or a float switch in the drain pan. The thermostat screen blank troubleshooter walks through each.
How to fix it
- If your thermostat takes batteries, replace them with fresh alkaline AA or AAA batteries of the same brand, matching the + and - marks.
- Check the breaker for the furnace or air handler and the power switch on or near it.
- Make sure the furnace or air handler door panel is fully seated. Never tape or bypass its door switch.
- If the screen is still blank, use the thermostat screen blank troubleshooter for the next checks.
If this does not fix it, tell the HVAC technician
- The thermostat screen is blank and the AC won't start.
- Whether you replaced the batteries and checked the breaker and door panel.
- The thermostat brand and model.
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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