Air Conditioning System Frozen Over
Discover causes of AC freezing, including low airflow, refrigerant issues, and improper settings. Follow steps to diagnose and fix a frozen AC unit.
1. Low Airflow
Restricted airflow prevents warm air from reaching the evaporator coil, causing it to get too cold and freeze.
• Dirty air filter
• Blocked return vents
• Closed or obstructed supply vents
• Dirty evaporator coil
• Blower motor issues
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2. Low Refrigerant
Low refrigerant causes pressure drops in the system, which makes the coil too cold.
• Often caused by a leak
• Signs may include ice on the outdoor line or hissing noises
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3. Thermostat or Fan Issues
• Thermostat set too low, especially during cooler nights
• Fan not running properly, so the coil doesn’t warm back up
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4. Running the AC When It’s Too Cold Outside
If it’s below ~65°F outside, many systems will freeze up, especially in shoulder seasons.
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What You Should Do:
1. Turn off the AC immediately to let it thaw (leave fan ON to speed it up).
2. Check and replace the air filter.
3. Make sure vents are open and clear.
4. Inspect for ice on the copper lines or at the coil.
5. Call an HVAC technician if it freezes again after thawing—it may be a refrigerant or blower issue.