Air Conditioner Leaking Water? Causes and How to Fix It

An air conditioner leaking water almost always comes down to the condensate system, the network that carries the moisture your unit pulls from the air safely outside. The common causes are a blocked or dirty condensate drain, a frozen evaporator coil caused by a dirty filter or low refrigerant, a cracked or overflowing drain pan, and poor installation that leaves the unit tilted the wrong way. Turning the unit off and cleaning the filter are safe to do yourself; refrigerant, coil, drain pan and electrical repairs are always a licensed technician’s job. This guide runs through each cause so you know which is which.

Water where it should not be is worth acting on quickly, because a slow leak can stain plaster, warp skirting and feed mould long before it looks serious.

Why is my air conditioner leaking water: the common causes

Your air conditioner is designed to produce water. As warm air passes over the cold evaporator coil, moisture condenses out of it, collects in a drain pan and drains away outside. An air conditioner leaking water inside the room means that normal flow has been interrupted somewhere. Here are the usual culprits.

A blocked or dirty condensate drain

This is the leading cause of an air conditioner leaking water. The condensate drain line carries collected water outside, and over time it clogs with dust, algae and slime. Once it blocks, water backs up past the drain pan and spills into the room. A split system leaking water from the indoor head, or a wet patch on the wall beneath it, very often points straight at a blocked drain line. Clearing the internal line is a technician’s job, but you can check the outdoor end yourself, which we cover below.

A frozen evaporator coil

If the evaporator coil ices over, it melts once the system stops, and the sudden rush of water overwhelms the drain pan and leaks out. A coil freezes for two main reasons: restricted airflow from a dirty filter, or low refrigerant from a leak. This is why a simple dirty filter can show up as an air conditioner dripping water rather than as weak cooling. Cleaning the filter is squarely a DIY task; if the coil keeps freezing after that, the refrigerant side needs a licensed technician.

A cracked or overflowing drain pan

The drain pan sits under the coil to catch condensation. On older units it can rust or crack, and once it does, water drips straight through instead of draining away. A misaligned pan can also simply overflow. Inspecting and replacing a drain pan means opening the unit, so it belongs with a technician rather than on the DIY list, but it is a common reason for an older air conditioner leaking water despite a clear drain line.

Poor installation or incorrect tilt

A split system’s indoor unit needs a very slight tilt so gravity feeds water toward the drain outlet. If it was mounted level or tipped the wrong way, condensation pools and escapes at the wrong end, and you get a split system leaking water from day one rather than after years of service. A ducted unit’s tray and pipework need the same correct fall. Fixing the mounting or the drain fall is installation work for a professional, and it is one reason a quality install matters from the start.

What you can safely check yourself

The safe DIY list here is deliberately short. First, if you find your air conditioner leaking water, turn it off at the wall to stop more water pooling and protect your floor and walls while you investigate. Second, take out the filter, clean it and let it dry fully, since a clogged filter is behind both airflow problems and a frozen coil. Third, walk outside and find the drain outlet, usually a small pipe on the wall near the outdoor unit, and check that water is dripping freely from it and that the end is not blocked by dirt or an insect nest. Those three steps are the full extent of what a homeowner should do, and they rule out the simplest causes.

When to call a licensed technician

Everything beyond turning the unit off, cleaning the filter and checking the outdoor drain outlet is a job for a licensed technician. Clearing a blocked internal drain line, repairing or replacing a cracked drain pan, correcting refrigerant that is causing a frozen coil, and fixing the tilt or mounting of a badly installed unit all need the right tools and, in the case of refrigerant and electrical work, a licence by law. Call a professional if the leak continues after you have cleaned the filter and confirmed the outdoor drain is clear, if the coil keeps freezing, or if you can see rust or damage in the tray. An air conditioner leaking water that you keep running risks damage to your home and, with electrics nearby, a safety hazard.

A leak and weak cooling often share a root cause, so if your unit is also struggling to cool, our companion guide on an air conditioner not cooling works through that side of the problem. Whether a split or a ducted system suits your home is a separate question, and our comparison of ducted air conditioning versus split systems covers it in detail.

Stop the leak and get it fixed properly

If you still have an air conditioner leaking water after the safe checks, the fault is inside the unit and needs a professional. Our licensed local team services and repairs air conditioners across Joondalup and the wider Perth area, north and south of the river, and we will trace the leak to its actual cause rather than patch over it. Browse our air conditioning Perth hub, see our split system air conditioners range, or call the team on (08) 6200 9718 for honest local advice.

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For help choosing the right system for your home, compare ducted air conditioning versus split systems, or talk to our Perth team about a service.