Air conditioner won't turn on?

If nothing runs when the thermostat calls for cooling, it's usually the thermostat, a tripped breaker or pulled outdoor disconnect, or a float switch tripped by a clogged condensate line. Check those before assuming a part has failed.

Not sure which one it is? Snap your ac and we’ll narrow it down.

Does it run but the air stays warm?

That's a cooling problem rather than a power problem. Air conditioner not cooling

Likely causes

Thermostat batteries, mode or setpoint
Most commonEasy DIY
A blank or dim display, not set to Cool, or the set temperature at or above the room temperature. A programmed schedule can also hold it off.
Part: $150–500 (if the thermostat itself has failed, installed)
Tripped breaker or outdoor disconnect pulled
Most commonEasy DIY
No sound or lights at either unit. Check the breaker panel and the disconnect box on the wall beside the outdoor unit.
Tripped float switch from a clogged condensate line
CommonModerate DIY
Water in the drain pan or on the floor near the indoor unit, with the system shut off. The float switch cuts power to prevent a flood.
Part: $75–250 (clear a clogged drain line); $100–500 (condensate pump)
Failed capacitor or contactor
CommonCall a pro
The indoor fan runs but the outdoor unit stays silent, or it hums or clicks without starting.
Part: $100–400 (capacitor, installed)
Failed control board
Less commonCall a pro
Power reaches the units and the thermostat is fine, but nothing responds, sometimes with blinking error codes on the indoor unit.

Quick checks

Switch off the breaker and the outdoor disconnect before touching the outdoor unit, and never reach into the fan. The capacitor stores a charge even with the power off, so capacitor and contactor work is for a pro. Refrigerant work needs a certified technician. Reset a tripped breaker once only; a breaker that trips again means a fault that needs a professional.

Check the thermostat: fresh batteries, mode on Cool, fan on Auto, and the set temperature below the room temperature.
Check the breaker panel and reset a tripped breaker once only. If it trips again, stop and call a pro.
Check the outdoor disconnect box beside the unit is fully in, not pulled out or switched off.
Look for water in the drain pan or around the indoor unit, which points to a clogged condensate line and a tripped float switch.
Heat pump? It's the same outdoor unit, so see the heat pump guide for winter-mode problems.

Sharpen the read

Diagnose your air conditioner in seconds, for free

No account, no phone number. Fixology’s AI reads your photo and tells you what’s likely wrong, how worried to be, and whether it’s a DIY fix.

Snap one of these:

the thermostat display and mode
the outdoor unit, including the fan and coil
the indoor unit and the area around it, especially any water
the model label on the outdoor unit

Add a note or more photos next. Nobody calls you.

When to call a pro

The breaker trips again after one reset, the outdoor unit hums or clicks without starting, power is on and the thermostat is fine but nothing responds, or you see water you can't trace. For lifespan and upkeep, see the air conditioner guide.

Typical cost: $250–700 for most repairs (about $375), up to about $3,000 when the compressor is involved. Expect a minimum service fee of about $75, hourly rates of $75–175, and $150–300 for emergency calls. If a repair passes half the replacement price, replacing is usually the better move.

Sources: Fixr: How much does AC repair cost? (updated January 29, 2026)

After a scan, Fixology can also help you find pros near you.