Frozen AC Lines or Coil? What to Do and Why It Happens

Quick answer

Ice on an AC's copper lines or indoor coil usually means too little airflow or low refrigerant. Turn cooling off, set the fan to On to help it thaw, and check the filter. If it freezes again after thawing, a technician needs to find the cause, which is often a leak or blower problem.

Key facts

Most common causes	Low airflow or low refrigerant
First step	Turn cooling off; set the fan to On to thaw
Watch for	Melt water near the indoor unit
Don't	Chip the ice or run cooling while it's frozen
If it refreezes	Have a technician find the cause

Why are my AC lines freezing up?

An AC coil freezes when it gets colder than it should. That usually happens when too little warm air moves across it, or when there isn't enough refrigerant in the system.

Other causes include a blower motor that's failing, dirt built up on the indoor coil, or running cooling on cool nights, when the coil can run colder than usual.

What should I do if my AC is frozen?

Thawing can take a while, depending on how much ice there is. Let it melt on its own.

1Turn cooling off at the thermostat.
2Set the fan to On. Moving air across the coil helps it thaw.
3Check the filter and replace it if it's dirty.
4Open any closed vents and clear blocked return grilles.
5Watch for melt water. Put towels down near the indoor unit, and look at the drain pan if you can see it without removing panels.
6Once all the ice is gone, turn cooling back on and watch. If ice comes back, turn cooling off and call a technician.

Don't chip, scrape, or heat the ice. The coil and copper lines are easy to damage, and a puncture means a refrigerant leak.

Not sure what's wrong yet?

Start with the safe checks. Many problems are a setting, a breaker, or a filter.

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What causes an AC to freeze?

Most freezing comes back to airflow or refrigerant. You can rule out the airflow causes at the top of this table yourself.

Cause	Why it freezes the coil	Can you check it?
Dirty filter	Less air across the coil, so it gets too cold	Yes
Closed or blocked vents and returns	Less airflow, same result	Yes
Dirty indoor coil	Dust blocks airflow and heat transfer	No
Low refrigerant from a leak	Pressure drops and the coil runs too cold	No. Certified technician only.
Blower motor or capacitor problem	The fan runs slow or not at all	No
Cooling on cool nights	The coil runs colder than usual	Yes. Set it higher or turn cooling off.

When should I call a technician about a frozen AC?

Call if the ice comes back after a full thaw and a clean filter, or if you can't find an airflow cause.

Ice returns after you turn cooling back on.
The indoor fan won't run.
Water is leaking beyond the drain pan.
You hear hissing or bubbling near the lines, which can be a sign of a leak.

What will a technician do about frozen AC lines?

A technician checks airflow first, then refrigerant. ENERGY STAR notes that airflow problems can reduce a system's efficiency by up to 15 percent, so fixing airflow helps with more than ice.

Blower speed and motor
Indoor coil condition
Refrigerant pressures, and a leak search if the charge is low
Ducts and returns for restrictions
The condensate drain, since melt water has to go somewhere

Is a frozen AC worth repairing?

Usually, yes: airflow problems and many leaks can be repaired. We fix what can be fixed — and tell you straight when it can't.

If a leak is in a coil that's worn out, we'll show you the repair price and the replacement option side by side. You'll hear the price before any work starts, and you decide.

Common questions

How long does it take a frozen AC to thaw?

It depends on how much ice there is. A thin layer can melt fairly quickly with the fan on, while a thick block can take hours. Keep towels down and let it melt on its own.

Can I run my AC while it's frozen?

No, running cooling on a frozen coil makes the ice worse and can strain the compressor. Turn cooling off and let it thaw first.

Why is there ice on the outside AC line?

Ice on the larger copper line at the outdoor unit usually means the indoor coil is freezing too. The same causes apply: low airflow or low refrigerant. Follow the thaw steps on this page.

Will a frozen AC fix itself?

The ice will melt, but the cause usually won't go away on its own. If it was a dirty filter, a new filter may fix it. If it freezes again, something else is wrong.

Is a frozen AC a sign of a refrigerant leak?

It can be, since low refrigerant is one of the most common causes of freezing once airflow is ruled out. A certified technician can check the charge and find the leak.

Why does my AC freeze on cool nights?

Some systems ice up when they run while it's cool outside, because the coil runs colder than usual. Try setting the thermostat higher or turning cooling off on cool nights. If it still freezes, have it checked.