Symptoms
- Vents blow air but it's warm or room temperature
- Problem may have started suddenly or gradually worsened
- Outdoor unit may be silent
Likely causes
- CommonOutdoor condenser unit not runningIf the outdoor fan and compressor aren't running, no cooling happens even though the indoor blower does.
- CommonFrozen evaporator coil that has since thawedA coil that froze and is now dripping water can leave you with only warm air until it's fixed.
- CommonLow refrigerantInsufficient refrigerant can't absorb enough heat, so air blowing over the coil stays warm.
- PossibleFailing compressor or capacitorWithout a working compressor, the system can't cool at all, though the indoor fan may still run.
- Less commonClosed or stuck damper in a zoned systemA zoning issue can route air away from where you're checking.
What to do
- Check that the thermostat is calling for cooling and not accidentally set to Heat or Fan Only.
- Check the outdoor unit; if the fan isn't spinning and you hear a hum, it likely needs a technician rather than DIY repair.
- Check the indoor coil for ice; if present, turn the system to Fan Only (not Off) to let it thaw before troubleshooting further.
- Replace the air filter to rule out restricted airflow as a contributing cause.
- If the outdoor unit runs normally and there's no ice, but air stays warm, suspect low refrigerant from a leak.
- Call a technician for refrigerant, compressor, or capacitor issues, since these require specialized tools and licensing.
Tools and parts
AC air filterSearch: “central air filter size replacement”
When to call a pro
Call an HVAC technician if the outdoor unit won't run or if warm air persists after ruling out ice and filter issues; refrigerant and compressor work needs a licensed pro.
Safety
Use caution
Refrigerant handling requires EPA certification; never attempt to add refrigerant yourself.