Aircon Freezing Up: Why Ice Forms and What to Do

Ice on an aircon is a symptom with three possible causes, and only one of them is something you can fix at home. If the ice comes back after a thaw and a clean filter, book an aircon check-up and repair visit: the technician checks the coil, the fan and the refrigerant level in one go.

Why a cold aircon makes ice

An aircon cools the room by passing warm air over a cold coil. Water in that air condenses on the coil and drains away, which is why a working unit drips outside. If the coil gets colder than it is meant to, that water freezes where it lands. The ice then blocks the air, the coil gets colder still, and the frost spreads.

• 1A clogged filter or a dirty coil. Less warm air crosses the coil, so it runs colder than it is meant to. The one to check first, because the filter is the part you can clean yourself.
• 2Low refrigerant. Refrigerant is not used up, so low means a leak, and with too little in the system the coil gets too cold.
• 3The fan is not moving enough air. A fan running slowly or not at all leaves the cold sitting on the coil.

The three causes

Not enough air across the coil

A clogged filter, a coil caked in dust, or something blocking the indoor unit. Both Carrier and TCL put restricted airflow first.

Low refrigerant

With too little refrigerant the coil runs too cold. A sealed system does not use refrigerant up, so low means it is leaking somewhere, and the fix is finding the leak. Topping it up without that is gas that will leave again. Why, in more detail: what freon is and why it should not need a refill.

A fan that is not doing its job

If the indoor fan runs slowly or stops, the cold stays on the coil. A failing fan motor, or the capacitor that starts it, can be behind it.

TCL adds two smaller ones: running the unit very cold on a cool night, and a faulty thermostat sensor that does not tell the unit to stop.

1. 1 Airflow is checked first, because a clogged filter is the common cause and the only one you can fix yourself.
2. 2 Low gas means a leak. Refrigerant is not used up, so the leak is found before any goes back in.

What to do when you find ice

1. Switch cooling off. On a split type, set the remote to fan mode, the fan symbol, so the fan keeps running with the compressor off.
2. Leave it. The moving air melts the ice. Carrier puts the thaw at one to four hours.
3. Put a towel or a basin under the indoor unit. Melting ice is a lot of water, and the drain may not keep up.
4. Do not use a hairdryer or a heater to speed it up. Carrier warns the sudden heat can crack parts.
5. Clean the filter while you wait, if you can reach it.
6. Switch cooling back on once the coil is clear. If ice comes back within a day or two, stop using it and book a check-up.

Stopping it coming back

Clean the filter every two weeks when the unit is used daily, keep the front of the indoor unit clear, and have the coils cleaned on schedule. TCL’s list is the same: clean filters, a clean fan, open vents, clean coils and a professional check. Ice that returns with a clean filter is not a cleaning problem.

Questions people ask

Why is my aircon freezing up?

Because the coil inside is colder than it should be, so the water it pulls out of the air freezes on it instead of draining away. The usual reasons are too little warm air crossing the coil, from a clogged filter or a dirty coil, low refrigerant from a leak, or a fan that is not moving enough air.

Will a frozen aircon fix itself?

The ice will melt if you switch cooling off, but the cause stays. Carrier is plain about it: a frozen aircon will not fix itself. Unless the cause was a filter you have now cleaned, the ice comes back.

Can I keep using an aircon that has ice on it?

No. It cools poorly while it is frozen, and Carrier warns that running it puts heavy strain on the compressor, the part the whole system depends on. Switch cooling off and let it thaw.

How long does a frozen aircon take to thaw?

Carrier gives one to four hours with cooling off and the fan running. A thick block of ice takes longer than a light frost.

Does a frozen aircon mean it needs freon?

Not always. Low refrigerant is one cause, and it means a leak, because refrigerant is not used up. A clogged filter or a dirty coil causes the same ice, and is checked first. The check-up finds out which before any gas goes in.

When to call us

If the ice returns, book an aircon check-up and repair. If the check-up finds a leak, the gas goes back in by weight after the leak is dealt with, through freon charging. If it finds a dirty coil, that is an aircon cleaning job.

Other guides

• Aircon capacitor: what it does and the signs it has failed

  The humming outdoor unit, the fan that will not spin, and why the capacitor is tested first.

• Aircon making noise: which sounds are normal and which are not

  Clicks and water sounds that are normal, and the rattles, hisses and squeals that need a technician.

• Aircon not turning on: what to check, and the 3-minute wait after a brownout

  Remote, breaker, the compressor’s restart delay, and the flashing lamp that means a technician.

• AVR for aircon: when you need one and how to size it

  What an AVR does in a brownout, which units already protect themselves, and sizing it from the nameplate.

• Aircon watts: how many watts a 1 HP aircon uses, size by size

  Running watts and kWh per hour for each size, how to read the nameplate, and starting watts for a generator.

• Types of aircon: split type, window type, portable and centralized

  How each is installed, how noisy and costly to run it is, which rooms suit it, and what a clean has to reach.

• What is freon, and why your aircon should not need a yearly refill

  The sealed loop, why low gas means a leak, the three refrigerants in Philippine units, and the refill myth.

• Aircon HP and room size: what each size cools, 0.5 to 2.5 HP

  The square metres each size suits in a shaded room and a hot one, with the arithmetic behind 0.6 HP.

• Aircon cleaning schedule: what to clean, and how often

  The filter every two weeks, a full clean by how hard the unit works, the deeper clean, and when in the year to book it.

• Common aircon problems, symptom by symptom

  Not cold, weak air, water inside, a smell, ice, noise, tripping and blinking: what each points to and what you can check.

• Aircon lifespan: how long it lasts, and repair or replace

  How many years a unit usually gives, what shortens it, and the signs that a repair is no longer worth it.

• Inverter vs non-inverter aircon: which costs less to run

  Kilowatt hours side by side at 2, 4, 8 and 12 hours a day, and the kind of use where a non-inverter is still fine.

• What size aircon for a bedroom, living room or kitchen

  Room by room: what each kind of room adds to the size you need, worked through for a sample two-storey house.

• Aircon energy saving tips that lower the bill

  Where the heat gets in, the setting and the fan, the timer, the cleaning, and reading the DOE energy label.

Sources: Carrier, “Will Frozen AC Fix Itself? A Guide To Frozen AC Coils”; TCL Philippines, “AC Freezing Up During the Winter? Here Are 7 Ways To Prevent It”.