Water dripping from a mini split head almost always means condensate is not draining. The unit pulls moisture out of the air as it cools, that water collects in a pan under the coil, and a small drain line carries it outside. Block the line, tilt the head, or freeze the coil, and the water finds another way out. Usually down your wall.
Where the water comes from
Any air conditioner makes water. Warm room air passes over a cold coil, moisture condenses on the fins, and it drips into a shallow pan built into the bottom of the head. From there a flexible drain hose runs out through the wall, bundled with the refrigerant lines inside the plastic line-set cover, and ends somewhere near the outdoor unit or at a small stub on the exterior wall.
Our air is dry, so a head in Pasadena, CA makes less water than the same unit would in a humid climate. It still makes plenty. A bedroom head running through an August afternoon produces a steady trickle, and it all has to go somewhere.
Some heads cannot drain by gravity. A head on an interior wall of a garage conversion, or one mounted lower than the point where the line exits the building, uses a small condensate pump. The pump has a float switch, a tiny reservoir, and its own ways of failing.
The usual causes, most likely first
A clogged drain line. Dust gets past the filter, settles in the pan, and washes into the line as a fine sludge. Add a little algae and the line narrows until it stops. Outside, the open end is a favorite spot for spiders and mud dauber wasps, and one Santa Ana wind event can pack the termination with grit. This is the cause more often than everything else combined.
A dirty filter that froze the coil. Starve the coil of airflow and it drops below freezing. Ice builds, the unit shuts down or you turn it off, the ice melts all at once, and the pan overflows. If you pull the front cover and see frost on the fins, this is it.
A head that is not level. The pan drains from one end. If the mounting plate went on with the drain end high, water pools at the far end and spills over the front. Old plaster walls in Altadena bungalows are rarely flat, and a plate installed without shimming tilts the whole unit.
A failed condensate pump or stuck float. You may hear the pump hum without moving water, or gurgle, or nothing at all. Some pumps have a safety switch that shuts the head down when the reservoir fills, so the symptom is a unit that stops cooling instead of a puddle.
A drain line routed wrong. Kinked inside the line-set cover, run uphill for a stretch, or looped so it traps water and air. This shows up on installs where the cover was crammed full or the line was run to a convenient spot instead of a downhill one.
Low refrigerant. A leaking system runs cold in the wrong places and ices the coil the same way a dirty filter does. If the head is dripping and also not cooling well, refrigerant moves up the list.
A loose or cracked drain connection. The drain hose slips onto a stub at the pan. It can pop off after someone cleans the head, or the pan itself can crack. Water then drips from inside the chassis rather than off the front edge.
Sweating refrigerant lines. Not the head at all. When the foam insulation on the larger refrigerant line is torn or sun-rotted, the cold copper sweats and drips. The drip track will lead to the line-set cover rather than the head.
What you can check yourself
- Turn the head off at the remote and let it sit long enough for any ice to melt.
- Pull the filter and clean it. Lift the front cover, slide the mesh out, rinse it, let it dry, put it back.
- With the cover up, look at the coil fins. Frost means airflow or refrigerant. Run fan-only mode for an hour or two to clear it.
- Find the drain termination outside. It is usually a short piece of clear or white tube exiting the wall near the line-set cover or ending near the outdoor unit. Check whether water comes out while the unit is cooling.
- Clear the outside end. Pull off any bug screen, mud, or debris. If you own a wet/dry vac, hold the hose tight over the termination for a minute. Suction from the outside end clears most sludge clogs without touching anything inside.
- Put a phone level on top of the head. Even a small tilt toward the wrong end matters.
- If there is a condensate pump, listen for it while the unit cools. Look for the small reservoir box in the line-set cover or on the wall and see whether it is full.
- Walk the line-set cover outside and look for bare copper or crumbled foam.
Skip the chemicals. Pouring bleach or drain cleaner into a mini split drain does more harm to the pan and hose than good.
When to call a licensed tech
- Ice comes back after a clean filter and a fan-only cycle.
- The head drips and the cooling is weak. That combination points at refrigerant, which needs a licensed contractor to find the leak, repair it, and recharge the system.
- The condensate pump has stopped or short-cycles.
- The head needs to be rehung level. It comes off the wall with the refrigerant lines still attached, and it is easy to kink a line or crack a flare fitting.
- The drain is clogged somewhere inside the wall chase and outside suction does not clear it.
- There is water staining on the drywall below the head, or a musty smell. Water has been getting behind the unit for a while, and a tech should see how far it went.
- Water has reached the electrical side of the head.
A drain that clogs every summer is a sign the head needs a proper coil and pan cleaning, which is mini split maintenance work. Anything involving refrigerant, the pump, or rehanging the unit is a mini split repair call.
Common questions
Is it normal for a mini split to drip outside?
Yes. That is the drain doing its job. In heating mode the outdoor unit also sheds water during its defrost cycles, which can look like a leak on a cold morning. Water on the ground outside is fine. Water on the wall inside is not.
Can I keep running the unit while it leaks?
Better not. Water on the drywall soaks in, and water inside the chassis finds the control board. Turn it off, or run it in fan-only mode, until the drain is clear.
Why does it only leak in the afternoon?
Because that is when the head is working hardest and making the most water. A partial clog handles the slow trickle of a cool morning and overflows when the afternoon flow rate goes up. It will get worse.
If your mini split is dripping and the outside end of the drain looks clear, we do a $69 diagnostic, credited toward the work, with a written quote before any work. Call Boost Services at 818-277-5056 between 6am and 10pm, seven days, or reach us here.
Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.