Noticing water dripping from your indoor aircon unit is one of those problems that demands immediate attention. Left unchecked, a leaking aircon can damage your ceilings, ruin wall paint, soak insulation in your roof cavity, and create the kind of mould problem that costs far more to fix than the original leak. Understanding the issue of Water Leaking From Your Aircon Unit is essential.
The good news is that most aircon water leaks have a clear cause — and once you know what you are dealing with, either you can address it yourself, or you know exactly when to call a professional before the damage spreads.
This guide covers every common reason your aircon is leaking water, what the risks are if you ignore it, and exactly what Perth homeowners should do about each one.
Water leaking from aircon units is one of the most frequent service calls we receive at Air Cool Care across Perth, particularly during the peak summer months of December through February. In most cases, the cause is straightforward — but the damage from ignoring it is not.
Is It Normal for an Aircon to Drip Water?
When Is Aircon Water Dripping Normal — and When Is It a Problem?
A small amount of condensation dripping from the outdoor unit of a split system is completely normal. As your aircon removes heat and humidity from the air, moisture condenses on the evaporator coil and drains away. On hot, humid Perth days, you may notice a trickle of water running from the outdoor unit — this is the condensate draining as it should.
What is not normal is water dripping or pooling from the indoor unit — the wall-mounted head unit inside your home. If you see water running down your wall, dripping from the front grille, or pooling on your floor directly below the indoor unit, something in the drainage system has failed.
For ducted systems, a blocked drain is even more serious. Water overflows from the drain pan into a safety tray in your roof cavity. If the safety tray drain is also blocked, the water has nowhere to go — and it ends up coming through your ceiling. In Perth homes with ducted systems, this kind of ceiling damage from a blocked condensate drain is a repair that can run into thousands of dollars.
Under Australian HVAC installation standards, condensate drain lines must be correctly sloped to allow gravity drainage. When systems are installed without adequate slope — or when drain lines sag over time — water backs up regardless of whether there is a blockage. This is an installation issue, not a maintenance failure, and it requires professional assessment.
What Are the Most Common Causes of Aircon Water Leaks?
Why Is Water Leaking From My Aircon Inside the House?
There are six main causes of water leaking from an aircon unit indoors. Each has distinct signs that help you identify which one you are dealing with.
Cause 1 — Blocked Condensate Drain Line
What Causes a Blocked Drain Line?
The condensate drain line is the most common source of indoor aircon leaks — particularly in Perth homes. Your aircon extracts moisture from the air as part of the cooling process. That moisture drips into a drain pan and flows out through the condensate line, typically a white PVC pipe that exits through an external wall or roof cavity.
Over time, dust, mould, algae, and debris accumulate inside the drain line and create a blockage. When the line is blocked, the drain pan fills up and overflows — and water starts running where it should not.
In Perth, this problem happens faster than in most other Australian cities. Perth’s dry, dusty summers mean that aircon systems pull significant volumes of fine dust through internal components. That dust mixes with condensation in the drain pan and forms a sludge that blocks drain lines more quickly than in humid coastal cities.
How to Fix a Blocked Condensate Drain
A mild blockage can sometimes be cleared using a wet-dry vacuum applied to the external drain outlet, or by carefully flushing the line with warm water. However, if the blockage is severe, or if water has already overflowed into a ceiling cavity or safety tray, professional service is the safer option.
A qualified technician will clear the blockage, flush the drain system, and inspect the drain pan for any damage caused by the overflow.
Blocked condensate drains are the single most common cause of water leak call-outs we receive across Perth during summer. Homes in the eastern and south-eastern suburbs — including Armadale, Gosnells, and Forrestfield — are particularly prone because the heavy dust loads from summer easterly winds accelerate the rate at which drain lines block. An annual pre-summer drain flush costs a fraction of what ceiling repair does.
Cause 2 — Dirty or Clogged Air Filters Causing Frozen Coils
How Do Dirty Filters Cause Water Leaks?
When your aircon filters become heavily clogged with dust, airflow across the evaporator coil is significantly reduced. Without adequate airflow, the coil gets too cold and ice begins to form on its surface.
The system continues to run, and as it does, the ice builds up. Eventually — either when the system switches off or when it cannot maintain the set temperature — the ice melts rapidly. The resulting volume of water far exceeds what the drain pan can handle, and water overflows onto your walls, floor, or ceiling.
Perth homes that run their aircon intensively through summer without cleaning the filters are particularly vulnerable to this. If your indoor unit has been dripping intermittently and you notice frost or ice visible inside the unit when you look through the grille, frozen coils from filter blockage are the likely cause.
How to Fix Frozen Coils from Dirty Filters
Switch the system off immediately and allow all the ice to melt fully before turning it back on — this typically takes one to two hours. Then clean or replace your filters. Once the filters are clean and the ice has completely melted, restart the system and monitor for further leaks.
Going forward, clean your filters every four to six weeks during Perth’s summer operating season. This is the single most effective preventative step you can take.
We will always tell you honestly if a leak was caused by a lack of filter cleaning rather than a component failure. Filter cleaning costs nothing and takes fifteen minutes. If that is all that was needed, we will say so — and show you how to do it yourself going forward.
Cause 3 — Cracked or Damaged Drain Pan
What Happens When the Drain Pan Fails?
The drain pan sits beneath the evaporator coil and collects condensation. Over time — particularly in older systems — the drain pan can develop cracks, corrosion, or holes. When this happens, water bypasses the drain line entirely and leaks directly from the unit regardless of whether the drain line itself is clear.
Plastic drain pans can crack from temperature stress or impact. Metal pans corrode over years of exposure to condensation. In either case, the pan can no longer hold water long enough for it to drain properly.
How to Fix a Cracked Drain Pan
A cracked or corroded drain pan requires professional replacement. This is not a DIY repair — accessing the drain pan requires disassembling part of the indoor unit, and the replacement must be the correct size and type for your specific system. A temporary sealant applied to a cracked pan will not hold under the volume of condensation a Perth summer generates.
Cause 4 — Refrigerant Leak Causing Coil Freezing
How Does a Refrigerant Leak Lead to Water Leaks?
When a system is low on refrigerant due to a leak, the pressure inside the evaporator coil drops. Lower pressure means lower operating temperature — and the coil freezes over, exactly as it does with blocked filters. As the ice melts, water overflows the drain pan and leaks into your home.
The key difference from a filter-related freeze is that cleaning the filters will not resolve it. If your system is freezing despite clean filters, reduced cooling performance, or if you notice a faint chemical or sweet smell alongside the leak, a refrigerant leak is the likely cause.
How to Fix a Refrigerant Leak
Switch the system off and contact a licensed HVAC technician immediately. In Australia, refrigerant handling is legally restricted to technicians holding an ARCtick refrigerant handling licence. The technician will locate the leak, repair the refrigerant circuit, and recharge the system to the correct operating pressure.
At Air Cool Care, our technicians hold the required ARCtick authorisation to handle, recover, and recharge refrigerants in compliance with Australian environmental protection regulations. Refrigerant handling by unlicensed individuals is illegal under Australian law and can void your system warranty.
Cause 5 — Incorrect Installation or Unit Not Level
Can Poor Installation Cause Water Leaks?
Yes — and it is more common than most homeowners realise. Split system indoor units must be installed with a very slight backward tilt so that condensation flows toward the drain outlet. If the unit was installed level or tilting forward even slightly, water pools at the front of the drain pan and drips from the grille rather than draining through the condensate line.
Similarly, if the condensate drain line was installed without adequate downward slope — or if the line has sagged over years — water will not drain by gravity and will back up into the pan.
How to Fix an Installation Issue
This requires a qualified HVAC technician to inspect the unit’s level, the drain line slope, and the overall installation against Australian standards. In some cases, the unit simply needs to be re-levelled. In others, the drain line routing needs to be corrected. Either way, this is not something to attempt without professional equipment.
Cause 6 — High Humidity Overwhelming the Drain System
Can Humidity Alone Cause an Aircon to Leak?
In Perth’s coastal western suburbs — including Cottesloe, Scarborough, Fremantle, and surrounding areas — summer days can bring sudden spikes in humidity, particularly when the sea breeze arrives in the afternoon. If doors and windows have been open and the home has absorbed humid air, switching on the aircon causes a rapid increase in condensation on the evaporator coil.
In most cases, this is a temporary situation — the system catches up once the indoor humidity normalises. The practical fix is to close all windows and doors before starting the aircon, rather than running it into an open, humid space.
However, if you regularly notice significant leaking during humid conditions even with the home closed, the drain pan or condensate line may have insufficient capacity for your system’s output — a professional inspection will confirm this.
What Are the Risks of Ignoring an Aircon Water Leak?
Is a Leaking Aircon Dangerous?
A slow drip may seem minor, but the secondary damage from an untreated aircon water leak can be severe. Water finding its way into ceiling cavities soaks insulation, causes plaster to swell and crack, and creates the damp conditions in which mould establishes itself rapidly. In Perth’s warm climate, mould in a ceiling cavity can spread across a large area within days if the moisture source is not addressed.
For ducted systems, the stakes are higher. A ducted system’s drain pan is located in the roof space. If that overflows, water can track across the ceiling and drip in areas of the house well away from where the AC unit is located — making the source harder to identify and the damage more widespread.
If water from a leaking aircon contacts electrical wiring or components — in the unit itself, in the ceiling cavity, or in a wall — it creates a genuine electrical hazard. If you see water pooling near any electrical outlet, switch, or wiring, turn the system off at the circuit breaker and contact a professional before touching anything.
How Can I Prevent My Aircon from Leaking Water?
What Maintenance Prevents Aircon Water Leaks in Perth?
Prevention is straightforward and far less expensive than repair. These are the specific steps that keep drain systems clear and leak-free across Perth’s demanding summer season.
Clean your filters every 4 to 6 weeks during summer. Clean filters maintain adequate airflow across the evaporator coil and prevent the freeze-thaw cycle that causes drain pan overflow.
Book a professional service annually before summer. A comprehensive pre-summer service includes a condensate drain flush, drain pan inspection, coil cleaning, and a check of the drain line slope. This single appointment prevents the majority of water leak call-outs.
Keep doors and windows closed before starting the aircon. This reduces the initial condensation load on the system, particularly on humid afternoons in coastal Perth suburbs.
Monitor the area around your indoor unit. A quick visual check once a week during heavy summer use takes seconds and catches early-stage leaks before they cause damage.
Act immediately when you see water. Switch the system off, identify the likely cause using this guide, and contact a professional if the cause is not immediately clear or if there is any risk of water near electrical components.
The Perth homeowners who avoid expensive water damage from aircon leaks are almost always the ones who book a pre-summer service and clean their filters regularly. It is genuinely that straightforward. The ones who call us for ceiling repair or mould remediation are the ones who noticed a small drip weeks earlier and decided to deal with it later.
Conclusion
Water leaking from your aircon unit is not something to monitor and hope resolves itself. Whether it is a blocked drain line, frozen coils from dirty filters, a damaged drain pan, or a refrigerant fault, the underlying cause will not fix itself — and the secondary damage compounds quickly in Perth’s warm climate.
The practical steps are clear: clean your filters regularly, book a professional pre-summer service, and act immediately when you see water rather than waiting. Most aircon water leaks are entirely preventable with routine maintenance — and the ones that do occur are far cheaper to fix when addressed early.
At Air Cool Care, our team has diagnosed and resolved aircon water leak problems across hundreds of Perth homes — from Joondalup in the north to Rockingham in the south, and from the coastal suburbs through to Armadale and the hills. We hold the required ARCtick refrigerant handling authorisation, work to Australian HVAC standards, and give honest assessments without upselling services you do not need. If your aircon is leaking water, contact Air Cool Care today.