AC wont turn on after storm - what should I check first?

VeteranHomeowner Veteran Jun 06, 2026

We had a pretty bad thunderstorm last night and now the ac wont turn on after storm. Furnace blower inside seems quiet too, and the thermostat is blank part of the time, then comes back on. No obvious burning smell, but the outside unit definitely is not kicking on.

I already checked the main panel and didn’t see anything that looked tripped, although I know sometimes they’re not obvious. Power in the rest of the house seems normal. I’m trying to figure out whether this sounds more like a blown fuse, thermostat issue, safety switch, or surge damage before I call someone out.

Storm included lightning and a brief power flicker
System was working normally earlier that day
Air filter was changed about a month ago

What would you check first in this situation?

ContractorDan_5aa3 · contractor Jun 07, 2026

Start simple. After storms, I usually see one of three things: tripped breaker, blown disconnect fuse, or low-voltage issue at the thermostat/air handler.

Check these in order:

Flip the AC and air handler/furnace breakers fully off, then back on
Look for the outdoor disconnect by the condenser and see if it’s seated right
If your thermostat goes blank, check the furnace/air handler power switch and any float switch near the drain line

If the thermostat is losing power, the outdoor unit may not be the main problem. Could be a 3-amp or 5-amp fuse on the control board, sometimes caused by a surge. If you’re not comfortable opening panels, this is where I’d get a licensed HVAC tech involved.

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MidwestMom · homeowner Jun 09, 2026

We had this happen in Ohio after a summer storm and I was convinced the whole AC was done for. In our case it was just a breaker that looked almost on, plus a little fuse inside the furnace control board. The thermostat had gone blank which sounds a lot like what you’re describing.

I’d check the cheap/easy stuff before paying for a full replacement pitch:

Breaker for outside unit
Breaker or switch for furnace/air handler
Condensate drain safety switch if you have one
Thermostat batteries, if that model uses them

If you do call someone, I’d get at least two quotes if they say surge damage hit major parts. We got very different opinions when ours happened.

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RetiredCarpenter · carpenter Jun 08, 2026

Old carpenter here, not an HVAC man, but I’ve chased enough storm troubles to know electricity can be sneaky. First thing I’d do is listen and observe. When you call for cooling, do you hear anything from the indoor unit? A click, a hum, even a faint one? If not, I’d suspect you lost control power somewhere rather than the compressor itself.

Another old-school check is to inspect around the outdoor unit for signs of a hard surge: scorch marks near the disconnect, a sharp electrical smell, or a wasp nest or debris jammed where it shouldn’t be. Also make sure the service switch by the furnace didn’t get bumped.

If the thermostat keeps going blank on and off, that points me back indoors. Storm may have knocked out a little fuse or board connection.

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