Your AC is running — you can hear it — but the house won't cool down. Here's what's usually wrong and what you can check yourself before calling.
This is the #1 cause. A clogged filter restricts airflow over the evaporator coil, and without enough air the coil freezes. Pull the filter out, hold it to a light — if you can't see through it, replace it and give the system an hour to recover.
If the system is low on refrigerant, cooling capacity drops. You might notice ice on the refrigerant lines or the outdoor unit. This usually means a leak that needs professional repair — adding refrigerant without fixing the leak is a temporary fix.
The outdoor unit rejects heat. If the coils are packed with dirt, grass, or cottonwood, the system can't dump heat efficiently. You can gently hose it down — but if it's been years, it needs a professional cleaning.
The compressor is the heart of the system. When it starts to fail, cooling weakens gradually. This is usually an expensive repair — we'll tell you honestly whether repair or replacement makes more sense.
Most common causes: dirty filter, low refrigerant, dirty outdoor coil, or a thermostat set to 'fan' instead of 'auto'. Check the easy ones first.
Filter and thermostat checks are free DIY. Anything involving refrigerant, electrical, or the compressor needs a tech.
Depends on the cause. Filter replacement is $5–$20. Refrigerant recharge with leak repair is $200–$600. Compressor replacement is $1,200–$2,500.