You notice it almost always the same way. A damp mark on the wall below the indoor unit, a few drops on the floor, or in worse cases a steady trickle while the unit is running. Don't panic. In most cases this is not a serious fault, but a condensate drainage problem. Here is what causes it and what you can check yourself before calling a technician.
Where the Water Comes From
When an air conditioner cools a room, it also removes moisture from the air. That moisture condenses on the indoor unit's evaporator and collects in a drain tray, from which a small pipe carries it outside. As long as that pipe is clear and has the right downward slope, water drains away without you ever noticing it. When something along the route gets blocked, the water has nowhere to go and backs up. Into the room.
The Most Common Causes
- Blocked drain pipe. The number one cause. Dust, dirt and sometimes algae clog the drain pipe, the water backs up and the tray overflows.
- Dirty filters. Clogged filters cause the evaporator to get too cold, ice forms on the coil, and when it melts, more water arrives than the tray can handle.
- Drain pipe installed at the wrong angle. If the drain pipe does not have sufficient downward slope from the unit, or worse has a reverse slope, water pools instead of draining.
- Low refrigerant charge. Insufficient refrigerant also causes the coil to ice up, with the same result as dirty filters.
- Running cooling in cool weather. Using the cooling mode when outdoor temperatures are already low can freeze the evaporator coil.
What You Can Check Yourself
Start by switching the unit off and mopping up. Then tackle the simple things first.
- Clean the filters. Open the front panel, rinse the filters under lukewarm water, let them dry fully before replacing them. This fix resolves the majority of cases, and in peak summer should be done every two to three weeks.
- Check the drain pipe outside. If no water is dripping from the pipe while the unit is running, the pipe is almost certainly blocked. Sometimes blowing into the pipe or gently sucking from the outer end is enough to clear it.
- Look for ice on the indoor coil. If you see frost, switch off and let it thaw. That is the sign of dirty filters or low refrigerant.
When to Call a Technician
If you have cleaned the filters and cleared the drain pipe and water is still leaking, the problem is deeper. A reverse-sloped drain pipe, a failed condensate pump or a refrigerant top-up are not DIY jobs. Ice that returns even with clean filters should not be ignored: running a unit with low refrigerant for long periods damages the compressor, the most expensive component in the system.
How to Prevent It
Regular maintenance prevents leaks in almost every case. Clean filters every two weeks during peak summer, a more thorough service at the start of the season, and a drain pipe check once a year. If your split unit is a few years old and has never been serviced, a professional clean at the start of summer protects you against both leaks and bad smells.