Symptoms
- Air blows but isn't cold
- Room stays warm on the lowest setting
- Unit runs constantly without catching up
- Weak airflow from the vents
Likely causes
- CommonDirty or clogged air filterBlocks airflow over the cold coil so the room never cools.
- CommonBlocked outdoor coil or finsDirt, leaves, or a bush against the back of the unit stops heat from escaping.
- PossibleUnit undersized for the roomA unit rated below the room's square footage runs nonstop but never catches up.
- PossibleLow refrigerant from a leakCoils feel only slightly cool while airflow stays strong; needs a technician.
- Less commonFailing compressorFan runs but no cold air is produced even after cleaning.
What to do
- Turn the unit off, remove the front filter, and wash it with warm soapy water or vacuum it; let it dry fully before reinstalling.
- Clear the front air intake and vents of furniture, curtains, or clutter that block airflow.
- Set the thermostat to its coldest setting and the fan to high, then let it run 20–30 minutes before judging results.
- Check the exterior coil and fins for leaves or dust and gently brush them clean.
- Confirm the unit's BTU rating matches the room size; an undersized unit will underperform no matter what.
- Feel the air from the vents: only slightly cool with strong airflow points to low refrigerant rather than a blockage.
- If the unit still blows warm air after cleaning, unplug it and call a technician.
Tools and parts
- Soft brush or vacuum
- Mild dish soap
Universal window AC filterSearch: “window air conditioner replacement filter”
When to call a pro
Call an HVAC or appliance technician if the coils are cool but the room never cools, since that usually means a sealed refrigerant leak that needs certified equipment.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.