August 26, 2026 · Cairns Aircon Installers
Water dripping from the indoor unit, a wet patch spreading across the ceiling, or a stain running down the wall below the head unit. In Cairns this is the fault we attend more than any other through the wet season, and it is almost never the mystery it looks like.
Where The Water Comes From
Your air conditioner is a dehumidifier as much as a cooler. Warm humid air passes over a cold coil, moisture condenses out of it, collects in a tray under the coil and drains away through a pipe to outside. In a Cairns February a single indoor unit can pull litres of water out of the air in a day.
So the water is meant to be there. A leak means it is not getting out the way it should.
1. A Blocked Condensate Drain
This causes the clear majority of leaks we attend here. The drain line silts up with a slimy biofilm of dust, mould and algae. Our humidity means that line is wet for months at a time, which is exactly the environment that sludge needs.
Once the drain blocks, the tray fills and overflows into your ceiling or down the wall. If the system has never been professionally serviced and it starts dripping in January, this is almost certainly why.
2. The Drain Line Has The Wrong Fall
A condensate drain relies on gravity. It needs a consistent downward fall the whole way to the outlet. If it was installed with a sag, a rise, or not enough slope, water pools in the pipe instead of running out, then backs up.
This one is an installation fault rather than a maintenance issue, and it tends to show up in the first wet season after a cheap install. Watch for it if the unit has always dripped occasionally rather than starting recently.
3. A Frozen Coil That Is Now Melting
If the coil ices up, then the ice melts, you get far more water than the tray was designed to handle all at once, and it overflows. The leak is the symptom; the ice is the actual problem.
Coils freeze because of restricted airflow (blocked filters, a filthy coil, a failing fan) or low refrigerant from a leak. If you have seen ice on the pipes or the indoor unit, that is what you are dealing with. Our guide on why systems stop cooling covers the causes.
4. A Cracked Or Displaced Drain Tray
Trays crack with age and UV exposure, or get knocked out of position during a clean or a repair. Less common than a blocked drain, but it does happen, particularly on older units.
5. Poor Insulation On The Pipework
Sometimes what looks like a leak from the unit is actually condensation forming on the refrigerant pipes themselves, where the insulation has gaps, has perished, or was never properly sealed at the joins. In our humidity, an exposed cold pipe will run with water. Follow the drip back to its source before assuming it is the tray.
What You Can Check Yourself
- Switch the system off.
- Find the outdoor drain outlet. On a humid day with the system running it should be dripping steadily. If it is dry while the indoor unit leaks, the line is blocked.
- Check the filters. Blocked filters cause the frozen coil that causes the flood.
- Look for ice on the pipework or the indoor unit.
Clearing a properly blocked drain is not a DIY job. People try to blow the line out and end up pushing the blockage further in, or forcing water back into the unit. It is a quick job for a technician with the right kit.
How To Stop It Happening Again
An annual service before the build-up is the whole answer. A proper service flushes the condensate drain, cleans the coil and tray, and checks the fall on the line. Book it in September to November and you go into the hard months with a system that will not put water through your ceiling.
If yours is leaking now, see our repairs service or get in touch. Turn it off in the meantime.