Symptoms
- Unit runs and blows air but it's not cold
- Room stays warm despite the unit running for a while
- Unit may cycle on and off oddly
Likely causes
- CommonDirty filter restricting airflowWindow unit filters clog quickly and are one of the most common causes of weak cooling.
- CommonThermostat dial set too high or in the wrong modeIt's easy to accidentally bump the dial or select Fan mode instead of Cool.
- CommonBlocked outdoor-facing coil (the back of the unit) from dirt or debrisDirt or leaves blocking the back coil prevent the unit from releasing heat properly.
- PossibleLow refrigerant from age or a slow leakWindow units can develop small leaks over years of use.
- PossibleFrozen coil inside the unitRestricted airflow can cause the coil to ice over, similar to central AC.
What to do
- Clean or replace the front filter, which usually slides out for rinsing or vacuuming.
- Confirm the thermostat dial is turned to the coldest setting and the mode is set to Cool.
- Check the back of the unit (from outside if possible) for dirt, leaves, or debris blocking the coil, and clear it gently.
- Turn the unit off and look inside the front grille for visible ice; if present, let it thaw before restarting.
- Make sure the unit is properly sealed in the window with no gaps letting outside heat in.
- If cooling stays poor after cleaning both coils and confirming settings, the unit likely has a refrigerant issue and may be more economical to replace than repair.
When to call a pro
Window units are usually not economical to repair for refrigerant issues; replacement is often the practical choice if cleaning doesn't help.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.