Ice on your air conditioner’s refrigerant lines or indoor coil means the coil is running below freezing, and that happens for one of two reasons: not enough warm air is moving across the coil (dirty filter, blocked vents, failed blower, dirty coil) or there isn’t enough refrigerant in the system (a leak). Turn the system off now, leave the fan running to thaw it, fix the airflow causes yourself, and call a technician for anything refrigerant-related — running an iced-up system risks flooding the compressor with liquid refrigerant, which is the expensive failure.
Right now
Set the thermostat to Off and the fan to On. This thaws the coil while moving air. Put towels or a shallow pan under the indoor unit; melting ice can overwhelm the drain. Don’t chip at the ice. While it thaws, work through the airflow checks below.
Airflow causes (fix these yourself)
Filter. The most common cause by far. A clogged filter starves the coil of airflow, the coil gets too cold, condensation freezes, ice restricts airflow further and the cycle runs away. Replace it. Filter guide.
Closed or blocked vents. Closing vents in unused rooms reduces airflow across the coil; open them. Check that furniture and rugs aren’t covering supply or return grilles.
Dirty indoor coil. If the filter has been neglected, the coil itself is likely furred with dust. That’s a technician’s job (chemical clean, $150–$400).
Blower problems. If little air comes out of the vents with a clean filter, the blower motor or its capacitor may be failing. Technician.
Running it when it’s cool outside. Below roughly 60–65°F outdoor temperature, many standard systems will ice up. Don’t run cooling on cool nights.
Refrigerant causes (call)
Low charge from a leak drops the pressure in the coil, which drops its temperature below freezing even with good airflow. Signs that point here rather than airflow: the filter is clean, air volume at the vents is normal, the system has been gradually cooling less over weeks, or you hear hissing at the indoor or outdoor unit. The fix is to find and repair the leak, then recharge; a recharge without a repair is a temporary and increasingly expensive patch. Prices and the R-410A cost picture are in refrigerant recharge cost. On a system past 10–12 years a coil leak is often the point where replacement makes more sense.
Less common: a stuck or failing metering device (TXV) or a partially collapsed line, which a technician will diagnose from pressures and temperatures.
After it thaws
Turn cooling back on with a clean filter and open vents. If it ices again within a day or two, stop running it and book a diagnostic; repeated freezing is a refrigerant or blower problem, and each cycle risks the compressor. Tell the technician when it started, whether the filter was dirty, and whether it re-froze after thawing; that narrows the diagnosis to minutes.
Costs
Filter change: $10–$40. Coil cleaning: $150–$400. Blower motor or capacitor: $130–$1,500. Leak repair and recharge: $600–$1,800+. Full ranges in the AC repair cost guide. If the system is not cooling but not frozen, start there instead. Every contractor on the North Carolina registry shows the license status we found.