Schedule soon
Ice on the refrigerant lines or the indoor coil means the coil is running below freezing. Almost always, too little air is moving across it (a dirty filter, blocked returns, a failing blower) or the system is low on refrigerant from a leak. Switch cooling off and run the fan only so the ice melts, then check the filter. If it freezes again, the cause needs a technician.
Turn the system off and call a technician if:
Melting the ice usually takes a few hours. Done this way it protects the compressor and sends the meltwater down the drain instead of onto the floor.
Set the thermostat to Off for cooling and the fan to On.
Moving air thaws the coil faster, usually within a few hours.
Replace the air filter.
The most common cause, and the easiest to fix.
Open supply registers and clear anything blocking return grilles.
The coil needs air from the whole house.
Once it has thawed, check that the drain is carrying the meltwater away, then restart cooling and look for ice again after an hour or two.
Ice that comes back means the cause is still there.
Ice is the symptom, and one of these is the cause. Pick one to see who can deal with it.
Common
You can check thisThe coil needs a steady flow of warm house air to stay above freezing. A clogged filter, furniture over a return grille or closed-off rooms starve it, and moisture on the coil turns to ice.
Common
Technician fixWhen refrigerant is low, pressure in the indoor coil drops, and its temperature falls below freezing with it. Ice often shows first on the larger, insulated copper line outside. The leak has to be found before the charge is corrected.
Common
Technician fixDust and biological growth on the coil fins insulate it and block air, which has the same effect as a dirty filter. Coils in humid climates collect growth faster.
Occasional
Technician fixA blower running slowly, or not at all while the outdoor unit keeps running, lets the coil freeze quickly. Weak capacitors and failing motors are common culprits.
Occasional
Technician fixIf the return side can't bring enough air back to the air handler, the coil sees too little airflow even with a clean filter. Crushed return flex in the attic is a frequent cause.
Follow the system from the coil that froze to the drain that has to carry it all away.
Field clip · 0:18
Field clip: an electronic leak detector is run along the copper tubing inside an outdoor unit to find where refrigerant is escaping.
Watch page & transcriptTurning cooling off and running the fan melts the ice in a few hours, and the system often cools normally again. That's why a frozen coil so often seems to fix itself overnight, then freezes again the next afternoon when the house is hot and the system runs for hours at a time.
Nothing about thawing changed the reason the coil got too cold. If the filter was the cause, a new one usually ends it. If ice comes back with a clean filter and open returns, either the coil is still short of air or the system is short of refrigerant from a leak. A dirty coil, a slow blower and crushed return ductwork are the usual airflow culprits. Each of those needs a measurement rather than another thaw, and running a system that keeps icing over is hard on the compressor.
A frozen coil gives false readings, so the ice has to be gone first. Then the cause usually shows up in one of these.
in. w.c.
High resistance on the return or supply side means too little air across the coil. It's compared with the maximum on the air handler's rating plate.
speed setting / µF
A blower on too low a speed, or with a weak capacitor, moves too little air even with a clean filter.
°F
Separates a low refrigerant charge from an airflow problem. From the outside, the two look alike.
Dust and biological growth on the fins insulate the coil and block air; in humid climates coils collect growth faster.
A technician makes sure the coil is fully thawed, then measures airflow (static pressure and blower operation) and the refrigerant charge using superheat and subcooling. If refrigerant is low, the leak is located before the charge is adjusted, and a dirty coil is cleaned. Free service call with repair.
Not responsibly. If refrigerant is low, there's a leak, and topping it up without finding the leak means the coil freezes again later. And if the real cause is airflow, adding refrigerant makes things worse.
Usually a few hours with cooling off and the fan set to On, and longer if the ice is thick. Keep an eye on the drain while it melts, because a lot of water arrives at once. Don't try to speed it up by chipping at the ice.
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