Symptoms
- Visible ice on the front coil when the cover is removed
- Weak or no airflow from the unit
- Water dripping heavily as the ice melts during off periods
Likely causes
- CommonDirty filter restricting airflowWindow unit filters clog quickly, and restricted airflow is the top cause of icing.
- CommonRunning the unit in cool outdoor temperaturesWindow units can ice up if run when it's cooler outside than they're designed for, especially at night.
- PossibleThermostat set to the coldest setting with low airflowRunning on max cold with a partially blocked filter increases the chance of icing.
- PossibleLow refrigerant from age or a small leakReduced refrigerant can cause the coil to run too cold and ice over.
What to do
- Turn the unit off and let it fully thaw, which can take a few hours; don't try to chip ice off yourself.
- Clean or replace the filter thoroughly once the ice has melted.
- Avoid running the unit on the coldest setting during cooler nights; use a moderate setting instead.
- Restart on a moderate cool setting and monitor for ice returning within the next few hours.
- If ice returns quickly even with a clean filter and moderate settings, suspect low refrigerant.
- Consider that older window units with recurring icing issues are often more cost-effective to replace than repair.
When to call a pro
If icing returns after a clean filter and moderate settings, replacement is often more practical than a refrigerant repair on an older window unit.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.