Symptoms
- Indoor unit runs but air isn't cold
- Room stays warm despite the unit being on for a while
- Outdoor unit may or may not be running
Likely causes
- CommonDirty indoor filter restricting airflowMini-split filters are washable and easy to clog, often needing cleaning more often than central AC filters.
- CommonWrong mode selected on the remoteIt's easy to accidentally select Fan or Dry mode instead of Cool.
- CommonOutdoor unit not runningIf the outdoor compressor unit isn't running, the indoor unit will only blow room-temperature air.
- PossibleLow refrigerant from a leakMini-split line connections can develop slow leaks over time.
- PossibleFrozen indoor coilSimilar to central AC, restricted airflow or low refrigerant can cause the coil to ice over.
What to do
- Confirm the remote is set to Cool mode, not Fan or Dry.
- Remove and rinse the washable indoor filter under water, letting it fully dry before reinstalling.
- Check the outdoor unit is running; you should hear a fan and feel warm air from it.
- Check the indoor unit's coil (behind the filter) for visible ice.
- If there's ice, switch to Fan mode to let it thaw before running Cool again.
- If cooling stays poor with a clean filter and running outdoor unit, the system likely needs a refrigerant check from a technician.
When to call a pro
Call an HVAC technician for a refrigerant check if cleaning the filter and confirming mode and outdoor operation don't restore cooling.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.