Frozen AC Coil
Quick Answer
A frozen AC coil happens when there's restricted airflow or low refrigerant. First, turn off the AC immediately to prevent compressor damage, then let it thaw for 2-4 hours with just the fan running. Check your air filter - a dirty filter is the most common cause.
Safe Checks You Can Do
- 1Turn off cooling immediately - Set thermostat to "off" or "fan only" to prevent further ice buildup and protect the compressor.
- 2Let it thaw completely - Run the fan only for 2-4 hours. Place towels under the unit to catch water. Don't chip at the ice.
- 3Check and replace the air filter - A clogged filter is the #1 cause of frozen coils. Replace it before restarting.
- 4Inspect vents and registers - Make sure all supply vents are open and unblocked by furniture or curtains.
- 5Check the blower - Listen for the indoor fan. If it's not running, the coil won't get enough airflow.
Likely Causes
- Dirty air filter
The most common cause. Restricted airflow causes the coil temperature to drop below freezing.
- Low refrigerant
A refrigerant leak causes pressure drops that lead to freezing. Requires professional repair.
- Blower motor problems
A failing blower can't move enough air across the coil, causing ice formation.
- Closed or blocked vents
Too many closed vents restrict airflow and can lead to freezing.
- Dirty evaporator coil
Years of dust buildup on the coil insulates it and causes temperature imbalances.
- Running AC when it's too cold outside
Most AC units shouldn't run when outdoor temps are below 60°F.
When to Call a Pro
- The coil freezes again after thawing and replacing the filter
- You suspect a refrigerant leak (hissing sounds, ice on the outdoor lines)
- The blower motor isn't running or makes unusual sounds
- This has happened multiple times in the same season
- You see oil stains near refrigerant lines (indicates leak)
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