You almost always notice it in the same way. A stain on the wall under the split unit, a few drops on the floor, or in the worst cases, a trickle that drips just as the device is running. No panic. In most cases, it’s not a serious fault but a condensation drainage problem. Let’s see what causes it and what you can check yourself before calling a technician.
Where all that water comes from
An air conditioner, when cooling, also dries the air. The humidity it removes from the room becomes condensation on the indoor unit and ends up in a tray, from which a small tube carries it outside. As long as this path is clear and sloped, the water flows out and you don’t even notice it. When something blocks the path, the water can’t find its way out and flows back inside the house.
The most common causes
- Clogged drain tube. This is the number one cause. Dust, dirt, and sometimes algae block the tube, water stops, and the tray overflows.
- Dirty filters. Clogged filters cause the unit to overcool, ice forms on the coil, and when it melts, more water arrives than the tray can hold.
- Improperly installed tube. If the drain isn’t properly sloped or has a reverse slope during installation, water pools instead of draining.
- Low refrigerant gas. An insufficient charge freezes the coil, the same effect as dirty filters.
- Excessive cold outside. Using cooling when it’s already cool outside can freeze the coil.
What you can check yourself
First, turn off the unit and dry the area. Then start with the simple things.
- Clean the filters. Open them, wash under lukewarm water, let them dry thoroughly, and put them back. This is the fix that solves most cases, and in summer it should be done every two or three weeks.
- Check the drain tube outside. If it doesn’t drip while the unit is running, it’s almost certainly clogged. Sometimes just blowing into it or gently vacuuming from the outer end can clear it.
- Look for ice on the indoor coil. If you see frost, turn off the unit and let it defrost. This signals dirty filters or low gas.
When to call a technician
If you’ve cleaned the filters and tube and water still leaks, the problem is deeper. A reverse slope in the tube, a broken condensate pump, or a gas recharge are not DIY jobs. And ice that returns even with clean filters shouldn’t be ignored: running for long periods with low gas damages the compressor, the most expensive part of the air conditioner.
How to prevent the problem
Regular maintenance almost always prevents leaks. Clean filters every two weeks in the height of summer, a deeper cleaning at the start of the season, and a tube check once a year. If your split unit is a few years old and has never been checked, a professional sanitization at the start of summer will protect you from leaks and bad odors.
Frequently Asked Questions
Can I use the air conditioner if it’s leaking water?
Better not until you understand the cause. Turn it off, dry the area, and check filters and tube. Continuing to use it while leaking damages walls and furniture and, if there’s ice on the coil, strains the compressor.
How much does it cost to repair an air conditioner water leak?
If it’s just the tube or filters, professional cleaning starts at a few dozen euros. If you need to recharge gas or replace the condensate pump, the cost rises, which is why it’s better to act early.
Why does it only leak water when it’s very hot?
In hot weather, the unit works harder and produces more condensation. If the drain is already somewhat clogged, on hotter days the tray overflows sooner.