A puddle under an indoor aircon unit is not something to mop up and ignore. In Brisbane’s humid conditions, your system can produce a surprising amount of condensation, but it should drain safely outside. Understanding why aircon leaks water helps you act before moisture damages plaster, flooring, stock, electrical components or the unit itself.
For a homeowner, a leaking split system can quickly become a ceiling or wall repair. For a café, office, venue or property manager, it can mean a slip hazard, disruption to customers and avoidable downtime. Some causes are simple to prevent. Others need a licensed air conditioning technician to diagnose and repair properly.
An air conditioner removes heat and humidity from indoor air. As warm, moist air passes over the cold evaporator coil, water vapour turns into liquid condensation. That water collects in a drain tray and travels through a condensate drain line to a safe discharge point.
The system is meant to make water. The problem starts when that water cannot reach the drain, the tray cannot contain it, or the coil freezes and later releases excess water. The location of the leak matters too. Water dripping from an outdoor unit on a hot day is often normal condensation. Water coming from a wall-mounted head, ceiling cassette, ducted grille or indoor cupboard is not.
Dust, slime, mould, insects and outdoor debris can build up in the drain line over time. Once the line is partially or fully blocked, water backs up into the drain tray and overflows through the indoor unit.
You may notice slow drips at first, a musty smell, water marks on the wall, or the unit stopping and starting if it has a safety float switch. In commercial systems, blocked drains can affect multiple indoor units or cause ceiling leaks well away from the actual blockage.
Clearing a drain is not always as simple as blowing into a pipe. The line needs to be checked for blockages, poor fall, disconnected joins and biofilm buildup. A technician can flush it safely and confirm the drainage route is working as intended.
A clogged return-air filter restricts airflow across the evaporator coil. With too little warm air moving over it, the coil can get cold enough to freeze. When the system cycles off or the ice melts, the drain tray receives more water than it can manage and overflow can follow.
Dirty filters are a common issue in homes with pets, construction dust or regular summer use. They also matter in businesses where doors are frequently opened, kitchens create airborne grease, or the system runs long hours.
Turn the unit off if you can see ice, feel very weak airflow or notice water leaking after the system has been running. Do not keep operating it in the hope that it will clear itself. Once the unit has thawed, clean or replace filters if appropriate, but arrange a service if freezing returns. A dirty filter may be the trigger, yet low refrigerant, a faulty fan or a dirty coil can create the same symptom.
The drain tray sits beneath the indoor coil and catches condensation before it enters the drain line. Age, corrosion, vibration and physical damage can crack the tray. In some ducted or commercial systems, trays can also rust through or sit incorrectly after previous work.
This type of fault often causes a consistent leak even when the drain line is clear. Because the tray is inside the unit, it is not usually a DIY repair. Accessing it may require dismantling covers, insulation or ductwork, and a temporary patch rarely lasts through another Queensland summer.
Condensate drains rely on gravity unless a condensate pump is fitted. If the indoor unit is not level, the drain line runs uphill, sags in sections or has been installed without enough fall, water can pool and spill back inside.
This can show up soon after a new installation, renovation or replacement system, although a pipe support can also fail years later. Ducted air conditioning is particularly vulnerable to concealed drainage issues because the pipework is often above ceilings. Water may appear at a light fitting or ceiling join rather than directly below the aircon.
A licensed technician should assess the installation rather than simply clearing the line. The lasting fix may involve regrading pipework, replacing a section of drain, fitting better supports or installing a correctly sized condensate pump.
Refrigerant is not consumed during normal operation. If a system is low, there may be a leak in the sealed refrigeration circuit. Low refrigerant can cause the evaporator coil to run too cold and ice up, which then creates water as it melts.
Faulty indoor fans, failed capacitors, sensor issues and heavily soiled coils can also reduce airflow and lead to icing. These are not faults to troubleshoot by adding refrigerant or removing panels yourself. Refrigerant handling and electrical repairs must be carried out by appropriately licensed technicians, and the underlying fault needs to be found before the system is returned to service.
Start by switching the aircon off at the remote or controller if water is actively dripping indoors. If water is near a power point, switchboard, light fitting or electrical wiring, avoid the area and arrange urgent professional help. Place a towel or bucket beneath the leak only where it is safe to do so, then move furniture, electronics, paperwork or stock out of harm’s way.
You can inspect and clean accessible filters in accordance with the manufacturer’s instructions. If the filters are heavily coated in dust, that is useful information for the technician. Check the outdoor drain outlet as well, provided it is safe and accessible. A small amount of water from that point during cooling is generally a good sign that condensate is draining.
Do not poke wire, pressure hoses or chemicals into a drain pipe. You can split a fitting, dislodge a concealed connection or force contaminated water back into the unit. Avoid running a frozen system, and do not remove electrical covers or attempt to repair a cracked tray.
A minor drip still deserves prompt attention, but some situations cannot wait for a routine appointment. Seek urgent air conditioning service when water is entering a ceiling cavity, dripping through light fittings, pooling near electricity, causing visible ceiling sagging, or affecting a business area used by staff or customers.
Commercial sites should also act quickly where a leak risks food storage areas, electrical equipment, server rooms, display stock or customer walkways. The cost of a drainage repair is usually far less than water-damaged ceilings, mould remediation, lost trading time or an injured customer.
For landlords and property managers, document the leak with photos, protect the area and organise a qualified repair without delay. Leaving an aircon leak until the next inspection can turn a manageable maintenance issue into a much larger building repair.
Regular maintenance is the practical way to reduce drain-related problems. Clean filters regularly during periods of heavy use, keep the outdoor unit clear of leaves and debris, and have the system professionally serviced at intervals suited to its workload. A lightly used bedroom split system and a commercial system operating through long trading hours do not have the same maintenance needs.
During a proper service, the technician can clean filters and coils, inspect the drain tray and line, test drainage, check airflow, identify early corrosion and look for signs of refrigerant or electrical faults. Preventative maintenance is especially worthwhile for ducted systems and commercial equipment, where a hidden leak can travel through ceilings before anyone sees it.
Kolda’s licensed technicians service residential and commercial air conditioning across South-East Queensland, with practical fault finding focused on fixing the cause rather than just stopping the visible drip. If your unit is leaking indoors, acting early protects the system, the building around it and the people using the space.
