An AC that runs without cooling is most often a dirty filter choking airflow, a failed capacitor, or low refrigerant from a leak. The filter you can fix in two minutes; a frozen coil means shut it off and let it thaw before a tech comes, or the real problem can't be diagnosed.
Likely causes
Clogged filter — Starved airflow freezes the coil and kills cooling — check this first, always.
Failed capacitor — The outdoor fan or compressor won't start properly; a common, relatively cheap repair.
Refrigerant leak — Ice on the refrigerant lines plus weak cooling. Refilling without fixing the leak buys weeks, not years.
Dirty outdoor condenser — Cottonwood, grass, and debris insulate the coil so heat can't escape.
What you can check yourself
Replace the filter. If the indoor coil is iced, turn the system off (fan on) for 3–4 hours to thaw.
Clear debris from around the outdoor unit — 2 feet of clearance on all sides.
Check that the thermostat is on 'cool' and below room temperature (it happens more than anyone admits).
Typical cost
Typical repairs in Portland, OR: capacitor $150–$350; refrigerant leak repair + refill $450–$1,200; fan motor $300–$600.
When to call a pro
Ice keeps returning, the breaker trips, or it blows warm after a filter change and thaw — those need a tech, and running it meanwhile can kill the compressor.
Data by Servik — verified local pros from official license records and public sources. Cost figures are typical ranges, not quotes; a pro's written estimate is the real number.