Why Is My AC Freezing Up?
AC freeze-ups are caused by restricted airflow or low refrigerant. The most common culprit is a dirty air filter, check this first. If your filter is clean, you may have low refrigerant (a leak), a failing blower motor, or dirty coils. Turn off cooling immediately when you see ice, run the fan to thaw, and call for service if it happens again.
Common Causes
Restricted Airflow
The most common cause. When airflow over the evaporator coils is reduced, usually due to a dirty filter, closed vents, or blocked returns, the coils get too cold and moisture freezes on them. Always check your filter first.
Low Refrigerant
Low refrigerant causes the pressure in the system to drop, which makes the evaporator coils colder than normal. This leads to ice formation. Low refrigerant always means a leak that needs repair.
Blower Motor Problems
If the blower motor is failing or running slowly, it can't move enough air across the coils. This reduces heat absorption and allows ice to form, even with a clean filter.
Dirty Evaporator Coils
Dust and grime on the coils insulate them from the warm air, causing them to get too cold. The layer of dirt traps moisture that then freezes. This happens gradually with neglected maintenance.
Thermostat Set Too Low
Running your AC at very low temperatures (especially below 70°F) when outdoor temps are moderate can cause freezing. The system was designed for temperature differentials, not absolute temperatures.
Collapsed Ductwork
Damaged or disconnected ducts in the attic or crawlspace can dramatically reduce airflow. This is often invisible but causes the same freeze-up symptoms as a clogged filter.
What Should You Do?
Try This First
- Turn off the AC immediately, continuing to run it can damage the compressor
- Set the fan to ON (not AUTO) to circulate warm air and help thaw the ice
- Check and replace your air filter
- Ensure all supply vents and return grilles are open and unobstructed
- Let the system thaw completely (2-4 hours) before turning cooling back on
Call a Pro If...
- The system freezes up again after thawing and replacing the filter
- You see ice on the refrigerant lines outside
- The system freezes frequently (more than once a season)
- You hear the compressor cycling on and off rapidly
- The blower fan seems weak or makes unusual noises