Why is my AC not cooling?
Short answer
The most common causes are a dirty air filter or frozen evaporator coil, a dirty outdoor condenser, low refrigerant from a leak, or a failed compressor or capacitor. Start with the filter and outdoor unit before calling for repair.
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Quick checks before you call
- Check the thermostat is set to Cool and below room temperature.
- Replace or clean the air filter if it's visibly dirty.
- Look at the outdoor unit — clear leaves, grass clippings, and debris from the coil.
- Check the indoor coil or lines for ice; if frozen, turn the system off and let it thaw fully before restarting.
- Confirm the breaker for the outdoor unit hasn't tripped.
Common causes compared
| Symptom | Likely cause | DIY-safe? |
|---|---|---|
| Warm air, filter dirty | Restricted airflow | Yes — replace filter |
| Ice on lines or indoor coil | Low airflow or low refrigerant | Thaw only, no DIY repair |
| Outdoor fan not spinning | Failed capacitor or motor | No — call a technician |
| System won't turn on at all | Breaker, thermostat, or control board | Check breaker only |
When it's an emergency
In extreme heat, with infants, elderly residents, or anyone with a heat-sensitive medical condition in the home, a fully non-functioning AC should be treated as urgent rather than something to schedule for later in the week.
What a technician checks that you can't
- Refrigerant charge and pressure with gauges, and whether there's an active leak
- Capacitor and compressor electrical readings
- Duct and airflow balance beyond the filter and vents
South Florida notes
South Florida systems typically run far more annual hours than units in milder climates, which shortens the practical service life of capacitors, contactors, and compressors and makes routine filter changes more important, since airflow restriction shows up faster under near-continuous runtime.
Related questions
Is it safe to add refrigerant myself?
No. Refrigerant handling requires EPA Section 608 certification, and adding refrigerant to a system with an undiagnosed leak doesn't fix the underlying problem.
Why does my AC run but blow warm air?
This usually points to a refrigerant issue, a failed compressor, or a problem on the outdoor unit rather than the indoor blower, which is why the outdoor unit is worth checking first.
Should I keep running the AC if the coil is frozen?
No. Running a frozen system can damage the compressor. Switch to fan-only or off and let it thaw completely, which can take several hours.
Sources
- Energy Saver: Air Conditioning — U.S. Department of Energy
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