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Ice on the air conditioner
Ice on the lines or the coil means the system is running too cold, and that is almost always airflow or refrigerant.
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The short version
- Most likely cause
- Not enough air moving across the indoor coil.
- Safe to do
- Switch cooling off, leave the fan on, and let the ice melt.
- Call a technician when
- It ices up again with a clean filter and open vents.
Safe to do yourself
- Turn cooling off at the thermostat and set the fan to on.
- Replace the filter if it is dirty.
- Open supply vents that have been closed.
- Put towels down where the meltwater will drip.
Stop and call
- Ice returns within a day or two.
- You hear hissing or bubbling near the lines.
- Water is coming through a ceiling.
- The system was topped up with refrigerant in the past.
Why a system freezes
- Low airflowA dirty filter, closed vents or a failing blower let the coil get colder than it should, and moisture freezes on it.
- Low refrigerantA leak lowers the pressure in the coil and its temperature with it. Adding refrigerant without fixing the leak only delays the next freeze.
- A dirty coilDust on the indoor coil acts like a blanket. Cleaning it is part of professional maintenance.
- Running in cool weatherRunning the system when it is cool outside can produce ice on its own.
What a technician will do
- Wait for a full thaw so readings are accurate.
- Check the filter, the blower and the coil.
- Measure the refrigerant charge.
- Fix the airflow problem or find and repair the leak.
Do not chip ice off the coil or the lines. The fins and tubing are thin, and a puncture turns an airflow problem into a refrigerant leak.
Related guides
Air conditioner running but not cooling
Air conditioner leaking water inside
AC compressor replacement: repair or replace the systemSources
- US Department of Energy