Quick Answer: An air conditioner that won’t power on at all — no lights, no response to the power button — is almost always an electrical or safety-switch issue, not a dead unit. Check that the outlet is actually live, then reset the LCDI plug (the in-line safety device most people mistakenly call a “GFCI plug,” required by UL on every portable and window AC sold since 2004), then check for a full condensate tank, which locks out the whole control panel on some models. If you just unplugged and replugged the unit, its built-in 3-5 minute anti-short-cycle delay may simply still be running. A blown thermal fuse or failed control board is possible but rare, and the last thing to check.
A unit that won’t cool is usually a maintenance problem — see our portable AC not cooling guide for that. A unit that won’t even respond to the power button is a different, narrower problem, and it’s almost never the compressor. Work through these six causes in order.
1. Confirm the outlet is actually live
Before touching the unit, plug a lamp or phone charger into the same outlet. A dead outlet — from a tripped breaker elsewhere in the panel, a GFCI outlet upstream that’s tripped, or simple wiring failure — presents identically to a dead AC, and it’s the fastest thing to rule out. If the outlet is dead, reset the room’s GFCI outlet (often in a bathroom or kitchen on the same circuit) and check the breaker panel before going any further.
2. Reset the LCDI plug — it’s not actually a GFCI
This is the cause almost everyone misdiagnoses. The bulky in-line plug on a portable or window AC’s power cord looks like a GFCI plug, and most owners call it that, but it’s actually an LCDI — Leakage Current Detection Interrupter. UL has required a factory-installed LCDI or arc-fault device on portable and window air conditioners manufactured since 2004 for a specific reason: these units have power cords that get pinched behind furniture, run through window sashes, or chewed by pets far more often than a typical appliance cord, and a damaged cord can arc and start a fire. An LCDI watches for that exact failure — leakage current as low as 5mA between the cord’s internal shield and its hot or neutral wire — and cuts power within half a second, which is a different job than the shock protection a wall GFCI outlet provides.
To reset it: unplug the unit fully, find the RESET button on the in-line plug itself (not the wall outlet), press it firmly until it clicks and stays down, then plug back in. If the button won’t stay depressed, or it trips again the moment you plug in, the cord has a genuine fault and needs replacing — this isn’t a repair you troubleshoot further.
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- If the LCDI plug won't reset or trips repeatedly, the cord — not the compressor — is the point of failure.
- Match the amp rating on the cord to your unit's nameplate spec before ordering.
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3. Check for a full condensate tank
Most portable units have a float-switch safety shutoff tied to the internal condensate tank, and it’s usually described as stopping the compressor once the tank fills. On some models, though, that same safety switch locks out the entire control panel — the unit won’t respond to the power button at all, not just refuse to cool — which looks exactly like a dead unit. Check the tank (usually accessible via a drain plug near the base) and empty it before assuming anything electrical is wrong. Our drain hose setup guide covers converting to a continuous gravity drain so the tank never fills unattended in the first place.
4. Rule out the anti-short-cycle delay
If the unit was just unplugged, tripped a breaker, or had a setting changed, many compressors and their thermostats build in a 3-5 minute delay before they’ll respond to a restart, regardless of what the power button does. The delay exists to let refrigerant pressure equalize inside the compressor — starting it against unequalized pressure causes real wear over repeated cycles, which is the same mechanism behind our short cycling guide’s restart-stress warning. If the unit seems completely unresponsive right after any power interruption, wait five minutes before concluding it’s broken.
5. Test without an extension cord
Most portable and window AC manuals explicitly warn against extension cords, and it’s not just a liability disclaimer — the LCDI plug in step 2 is calibrated to the exact cord length and gauge the unit ships with, and a longer or thinner extension cord can cause enough voltage drop to either prevent the compressor from starting or trip the LCDI on its own. If you’re running one, plug the unit directly into a wall outlet instead. If it powers on there, the cord was the problem, not the AC. Our surge protector guide covers the one type of add-on cord that’s actually rated for AC compressor loads, if you need surge protection without extending the run.
6. Check for a control lock or a frozen control board
A few remaining causes, roughly in order of how often they show up: a control lock (sometimes a small padlock icon on the display) engaged accidentally, which blocks the power button specifically to prevent kids or pets from changing settings — check your unit’s manual for the lock/unlock button combination, since it varies by brand. Next, a control board that’s frozen rather than failed, usually from a brief power blip; a full unplug for 60 seconds (longer than the anti-short-cycle delay in step 4) often clears this the same way restarting a router does. Least likely of all: a blown thermal fuse or a genuinely failed control board, which doesn’t respond to any of the above and does mean the unit needs a technician or replacement.
The bottom line
Check that the outlet is live, then reset the LCDI plug — the safety device almost everyone mistakes for a GFCI, required on every portable and window AC since 2004 — before assuming anything else is wrong. A full condensate tank can lock out the whole control panel on some models, not just stop cooling, and a 3-5 minute anti-short-cycle delay after any power interruption can make a working unit look dead for a few minutes. Rule out an extension cord next. Only a control lock or a genuinely failed control board — the rarest causes here — need anything beyond a reset or an empty bucket.
Confirmed the unit is actually dead? Start with our best portable air conditioner guide. If it powers on but won’t cool, that’s a different, more common problem — see our portable AC not cooling guide. And if it powers on but keeps shutting off every few minutes, see our short cycling guide.