Symptoms
- Visible ice or frost on the indoor coil or refrigerant lines
- Weak or no airflow from vents
- Water pooling near the indoor unit as ice melts
Likely causes
- CommonDirty air filter restricting airflowReduced airflow over the coil lets it get too cold and ice over.
- CommonBlocked or closed supply/return ventsSimilar effect to a dirty filter: less air moving means the coil freezes.
- CommonLow refrigerant from a leakLow refrigerant pressure causes the coil to run colder than designed, leading to ice.
- PossibleFailing blower motor or fan speed too lowInsufficient air movement across the coil has the same freezing effect as a dirty filter.
- PossibleRunning the AC in cool weather or overnight with low loadVery low outdoor temperatures or light use can sometimes cause icing even with a healthy system.
What to do
- Turn the thermostat to Off, but leave the fan on Fan Only (not Auto) to help the coil thaw faster.
- Replace the air filter if it's dirty.
- Check all supply and return vents are open and unblocked.
- Let the system thaw completely, which can take several hours, before restarting cooling mode.
- Once thawed and restarted, watch for ice returning within a few hours, which points to airflow or refrigerant as the ongoing cause.
- If ice keeps returning after a filter change, call a technician to check refrigerant levels and the blower.
Tools and parts
AC air filterSearch: “central air filter size replacement”
When to call a pro
Call an HVAC technician if the coil freezes again after a filter change and open vents; low refrigerant is a common repeat cause.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.