AC frozen? Ice on the lines or coil
Ice on the copper lines outside or on the indoor coil means the air conditioner is freezing up, usually because not enough warm air is moving over the coil. A clogged filter is the most common cause. Thaw it first, fix the airflow, and it often runs fine again. Resist the urge to chip the ice off. The fins underneath bend easily, and turning the system off and letting it melt on its own does the job without the damage.
Why an AC freezes up
The indoor coil gets very cold as it cools the air. Normally the warm air blowing across it keeps it just above freezing. With too little airflow, from a dirty filter or closed vents, moisture on the coil freezes and the ice builds.
Low refrigerant can also cause freezing. That's a leak that needs a licensed technician, but it's worth ruling out the airflow problems first.
What makes an AC ice over
Too little air over the coil.
Airflow drops.
A leak; needs a technician.
The blower isn't moving enough air.
| What you find | Likely cause | Fix |
|---|---|---|
| Filter is gray and clogged | Low airflow | Replace the filter. |
| Vents closed or blocked | Low airflow | Open them. |
| Ice returns with a clean filter | Low refrigerant or fan | Call a technician. |
| Only freezes at night | Set too low for cool weather | Raise the setting. |
Thaw it, then fix the airflow
- Turn the cooling offSet the thermostat from COOL to OFF, and switch the fan to ON. The fan blows room air over the ice and speeds up thawing.
- Let it thawIt can take several hours, sometimes most of a day. Put towels around the indoor unit in case the drain pan overflows. Don't chip at the ice; you can damage the coil.
- Change the Replace the filter with a clean one of the right size, arrow pointing toward the unit. A clogged filter is the most common reason an AC freezes.
- Open the ventsMake sure the supply vents in every room are open and not covered, and that return grilles aren't blocked by furniture or curtains.
- Check the Once the ice melts, make sure the water drains away. If the drain pan is full, the line may be clogged and need clearing.
- Restart and watchWhen there's no ice left, set the thermostat back to COOL. After an hour, look at the lines and the unit again. If frost comes back, turn it off and call a technician.
Watch it done
- No frost on the lines or unit an hour after restarting
- Melt water drains away and the pan isn't full
- Cool air comes from the vents
If the ice comes back
If it only freezes on cool nights, the thermostat may be set lower than the system can handle when it's cool outside. Raise the setting a few degrees at night.
If the indoor coil itself is caked with dust, cleaning it is usually a job for a technician.
What a pro typically charges (a rough estimate; prices vary by area): An AC service call typically runs $100–$300. Finding and fixing a refrigerant leak often costs several hundred dollars or more.
Find an HVAC technician near you