Symptoms
- Air moves but has no cooling effect at all
- Was cooling fine recently and stopped suddenly
- Compressor doesn't seem to be running (no hum)
- Warm air even right after turning the unit on
Likely causes
- CommonUnit accidentally set to fan-only modeFan mode moves air without running the compressor, so nothing gets cooled.
- CommonSeverely clogged filter or blocked outdoor coilExtreme blockage can prevent the compressor from cooling effectively.
- PossibleCompressor not startingListen for the deeper hum of the compressor separate from the fan; if it's silent, the compressor isn't engaging.
- PossibleComplete loss of refrigerant from a leakNo cooling at all with the compressor running points to a fully lost charge.
- Less commonFailed compressorThe compressor motor has burned out or seized.
What to do
- Check the mode setting on the unit or remote and make sure it's set to Cool, not Fan.
- Set the temperature well below room temperature and fan to high, then listen for the compressor's deeper hum starting up.
- Clean the filter and check the outdoor coil for severe blockage as described in the cooling and airflow guides.
- Let the unit run 15–20 minutes and feel the air again; also feel the outdoor exhaust, which should feel warm if the compressor is working.
- If the compressor never engages (no deep hum, only fan noise), the issue is electrical or a failed compressor.
- If the compressor runs but the air stays warm, refrigerant loss or compressor failure is likely.
Tools and parts
- None
When to call a pro
Call an HVAC technician if the compressor isn't engaging or runs without producing cold air, since diagnosing refrigerant or compressor issues needs specialized tools.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.