You switch the aircon on, and a few hours later the room is warm again. You look up and there is frost on the indoor unit: a white crust on the louvres, a fur of ice on the copper pipe, or a block of ice behind the front panel. Then you switch it off, and ten minutes later water is running down the wall.
Ice is a symptom. It tells you the indoor coil has been running colder than it should, for long enough to freeze the moisture it collects. This guide covers what to do in the first ten minutes, how to thaw the unit without damaging it, the two usual reasons the coil gets that cold, what you can safely check yourself, and when to book a visit.
First ten minutes: what to do right now
- Stop cooling. Switch the unit from cool to fan-only mode, or off. Running the compressor against a frozen coil gives you little cooling anyway and can make the underlying problem worse.
- Let it thaw. Fan-only mode moves room air across the coil and melts the ice faster than leaving the unit off. Expect a lot of water while it melts.
- Catch the water. Put a towel or a shallow tray under the unit and move anything under it that water could damage. Meltwater can drip from places the drain pipe does not serve.
- Do not chip or scrape the ice. The fins are thin metal and the copper pipe joins are not built to take knocks. Let it melt.
- Do not restart cooling until it is completely clear. Wait until there is no ice on the coil, the louvres or the pipe, and the dripping has stopped.
If you switch cooling back on and the ice returns within a few hours, do not keep cycling it. Something is making the coil too cold, and that needs finding, not thawing again.
Why an aircon freezes: the two usual reasons
The indoor coil is meant to get cold, but not so cold that the moisture on it freezes. Two things push it past that point.
1. Not enough air moving across the coil
The coil relies on room air flowing over it to carry the cold away. If that airflow drops, the coil keeps getting colder. Common reasons:
- A clogged filter, or a coil coated in dust and grease.
- A blower wheel caked with dirt, or a fan that is slow or struggling.
- Furniture, curtains or a bed placed right in front of the unit.
The filter is the one you can check yourself. Our guide to washing aircon filters yourself and where DIY stops covers how to do it safely. A coil or blower wheel behind the filter is a different matter: a general service does not always reach it, which is covered in what a general service does not reach.
2. Not enough refrigerant
Refrigerant is not used up. It circulates in a sealed loop, so a system that is low on gas has lost it somewhere. Our gas leak repair page lists ice on the copper pipes or the indoor coil among the signs of a leak, and notes that when the ice melts it drips and looks like a water leak. The related signs it lists are cooling that fades gradually over weeks, a hiss from the unit or the piping, and a previous top-up that did not last.
The two causes look the same from the outside: both give you ice. What separates them is what happens once the airflow is sorted. If the unit still ices up after a clean filter and a clear path in front of it, the gas side needs to be checked.
A quick self-check before you call anyone
Once the unit is completely thawed and dry, work through this in order. None of it involves opening the unit beyond the front panel.
- Look at the filter. Flip the front cover up, slide the filter out and hold it to the light. If you cannot see through the mesh, wash it, dry it fully and refit it.
- Look at what is in front of the unit. Clear the airflow path in front of the louvres.
- Check the drain. If the dripping carried on long after the ice had gone, or water is coming out of the unit rather than the drain pipe, read aircon water leaking: causes and how to stop it.
- Restart in cool mode and watch it. Check the louvres and the copper pipe after an hour or two. If frost appears again, stop.
If the unit ices up again after a clean filter and a clear airflow path, the cause is not the filter. Do not wash it again and try a third time.
What not to do
- Do not keep running it "to see". A frozen coil delivers little cooling, and our gas leak repair page warns that running low on gas overworks the compressor, the most expensive part of the system.
- Do not keep topping up gas. If a top-up only helps for a while, you are renting gas. Our guide on how to tell if your aircon needs a top-up or a leak repair explains why a system that keeps losing gas needs the leak found.
- Do not use a hairdryer or hot water on the ice. Let the fan do it.
- Do not open the unit further than the front panel. Electrical parts sit behind it.
What a visit involves and what it costs
These are the published prices on aircons.sg. The price you see is the price you pay.
- Service visit plus the 9-point pre-check, including a gas pressure check: $45. It is waived if you proceed with a gas top-up.
- General servicing: $45 for 1 unit, $70 for 2, $95 for 3, $115 for 4, and $25 per unit from 5 units.
- Chemical wash: $135 for 1 unit, $245 for 2, $345 for 3, $425 for 4, and $100 per unit from 5 units, for a coil that is fouled beyond what a general service reaches.
- Gas top-up: R22 $115, R410A $130, R32 $170, priced per outdoor circuit.
- Pressure test of the piping set: $150 per FCU, if the leak needs to be pinpointed.
- Piping replacement: $450 per FCU. A joint, a corroded coil or concealed pipe work is quoted upfront after the test, before any work starts.
- Standard repairs such as drainage or electrical faults: from $80.
The visit tells you which of these applies. If the pre-check finds a dirty coil or a choked drain, the fix is a service, a wash or a drain repair. If it finds low pressure, the question becomes where the gas went, which is what the pressure test is for. You see the finding and the price before any work starts, and repair work carries a 90-day workmanship warranty. More on the gas side is on the gas leak repair cost page and the pressure test page, and every price sits on the pricing page.
What to tell us when you WhatsApp
You will get a faster and more accurate answer if you send:
- Where the ice was: louvres, front panel, coil or copper pipe.
- How long the unit had been running before it appeared.
- Whether it came back after you cleaned the filter.
- A photo of the ice, and one of the outdoor unit's nameplate sticker, which shows the refrigerant type.
- How many units the home has, and which room this one is in.
Ice that comes back after a clean filter is a reason to book a check rather than a reason to keep experimenting.
WhatsApp us on 9107 2601 with a photo and the number of units.