Split AC Leaking Water Inside? Causes and Fixes in Oahu Homes

01Where the water comes from

An air conditioner dries the air while it cools it. Moisture condenses on the cold indoor coil, drips into a pan underneath and runs out a thin drain line. Usually that line goes through the wall to the outside. Sometimes it goes to a small pump.

In Phoenix that line might barely trickle. Here it can run for hours, especially on the Windward side or in a condo that's been closed up all day. Because the inside of the line never dries out, mold and algae grow in it until there's a soft plug of sludge. Water backs up into the pan, the pan fills, and eventually it spills over the front edge of the unit and down your wall.

02What usually causes it

Most of the time it's the drain line. It clogs slowly, so a unit can run fine for months and then start dripping during a sticky week when it's running nonstop. Clearing it properly means flushing the line and cleaning the pan as well. Leave the pan dirty and the sludge in it washes right back into the line, and you're calling again a month later. One Makakilo customer's line was packed solid with mold. Once the system was cleaned and the line cleared, the leak stopped and hasn't come back.

If you see frost on the copper pipes or on the coil behind the filter, you're looking at meltwater. A unit with a frozen coil tends to drip after it shuts off rather than while it's running. A filthy filter is the easy explanation. If the filter's clean and the ice keeps coming back, a slow refrigerant leak or a blower problem is more likely, and our guide on why an AC freezes up goes into both.

A brand-new unit that's leaked since day one is usually tilted slightly backward, or its drain line runs uphill somewhere inside the wall. That's a call back to whoever installed it.

Older units can develop cracked or rusted pans. We had a Mililani job where clearing the line didn't stop the drip at all, and the pan turned out to be cracked underneath.

Indoor units on interior walls, which you see a lot in condos, can't drain by gravity, so they use a small condensate pump. When the pump dies or its float sticks, water overflows fast. Some pumps have a safety switch that cuts power to the AC, which means the first thing you notice may be the AC quitting, with the water coming later.

03Things you can check yourself

Pull the filters out from under the front panel and rinse them in lukewarm water. Let them dry before they go back in.

Look at the copper lines where they enter the indoor unit and at the coil fins behind the filters. If there's frost, leave the AC off for a few hours with towels down, then run it on fan only.

Go outside and find where the drain line ends. After the AC has been running for 20 minutes or so on a humid day, it should be dripping. If it's dry, the line is probably clogged.

Make sure that outside end isn't kinked, buried in mud or stuffed with leaves. Geckos and bugs like to move into it.

If you have a condensate pump, listen for it. It should run for a few seconds at a time. A silent pump with water pooling, or one that's beeping at you, needs a look.

04If you live in a condo

Water from a leaking head in a tower doesn't stay in your unit for long. It gets into the wall and the slab and can turn up in your neighbor's ceiling, and that's how a cheap drain cleaning turns into an insurance claim. Deal with it the day you see it.

Most buildings also want a licensed, insured contractor for any AC work, so check the house rules before anyone shows up with tools. Our condo and high-rise AC service takes care of building access, insurance certificates and AOAO coordination. If you're adding or replacing a unit, the AOAO approval guide covers the paperwork.

05Keeping it from coming back

Nearly every drain leak can be prevented by keeping the unit clean. A split AC deep cleaning takes the buildup off the coil, blower wheel and pan and flushes the line, so the sludge actually leaves the system instead of getting pushed further down the pipe.

How often you need one depends on where you live and how much the AC runs. A bedroom unit in Kaneohe that runs every night needs a lot more attention than a guest room unit in Ewa that gets switched on twice a month. Our guide on how often to clean a mini-split in Hawaii has the details. If you've noticed a musty smell along with the leak, it's probably the same buildup; why your AC smells musty explains the connection.

If you'd rather not keep track yourself, Comfort Club members get two cleanings and tune-ups a year on a schedule.

06When to call us

Still dripping after you've cleaned the filter and checked the outdoor drain? That's the point to book a tech. The same goes for ice that comes back with a clean filter, a new unit that's leaked since install, a pump that won't run, or water that's reaching your walls, floor or the unit below.

We'll track down what's causing it, show you photos of what we find, and give you a flat price before any work starts. Call or text (808) 400-6593, or book a split AC repair online.

We fix leaking split ACs all over the island, including Kaneohe, Makakilo and Pearl City. You'll find more on our split AC repair page.