Air Conditioner Not Cooling — DIY Checklist Before You Call
When the AC runs but the house won't cool, most causes are simple and free to fix. Go through this list in order before calling a tech — you'll solve it yourself most of the time.
Thermostat, Filter, and Power
Set the thermostat to COOL and a few degrees below room temp, and check it isn't on 'fan only' or running on dead batteries. Then check the air filter — a clogged filter is the single most common cause of weak cooling and can even freeze the system. Replace it if it's gray. Finally, confirm both breakers (the indoor air handler and the outdoor unit have separate ones) are on; a tripped breaker stops cooling while the fan still runs.
Check for a Frozen Coil
If air barely comes from the vents, the indoor evaporator coil may be iced over — caused by a dirty filter, blocked vents, or low refrigerant. Turn the system to OFF (or FAN ONLY) and let it thaw for a few hours, then replace the filter and make sure return and supply vents are open and unblocked. If it freezes again right away, that points to a refrigerant or airflow problem that needs a tech.
Clean the Outdoor Condenser
The outdoor unit dumps your home's heat, and it can't if it's choked with grass, leaves, or dirt. Shut off its breaker, rinse the fins from the inside out with a gentle hose stream (never a pressure washer), clear at least 2 feet around it, and straighten bent fins. A filthy condenser is a top reason an AC runs constantly but never satisfies. If everything here checks out and it still won't cool, you likely have a refrigerant leak, a failed capacitor, or a compressor issue — that's the point to call a pro.
Parts & Tools
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FAQ
Most often a dirty filter, a frozen evaporator coil, a tripped outdoor breaker, or a dirt-choked outdoor condenser. Work through those first; if they're all clean and set right, suspect low refrigerant or a failed capacitor and call a tech.
Check the thermostat is on COOL (not fan), the outdoor unit's breaker is on, and the filter isn't clogged. Warm air with the outdoor fan not spinning often means a tripped breaker or a bad capacitor.
Turn the system off and let it thaw for a few hours, replace the air filter, and open all vents. Ice is usually caused by restricted airflow or low refrigerant; if it refreezes, have it checked.
Sources
Documents this guide was checked against. How we verify.
Always unplug an appliance and shut off its water supply before servicing. This guide is informational and not a substitute for a qualified technician.