There are few things more frustrating than walking into your Perth home on a scorching summer afternoon, feeling a drip on your shoulder, and realising your air conditioner is leaking water inside. It’s alarming. It’s messy. And if you ignore it, it can quickly turn into something much more serious than a puddle on the floor.
The good news? In most cases, an air conditioner leaking water is a problem that can be diagnosed, understood, and fixed — especially when you know what you’re looking at.
This guide covers everything Perth homeowners need to know: why it happens, what each cause means, which fixes you can do yourself, and when it’s time to call in a licensed technician.
Why Is Your Air Conditioner Leaking Water Inside?
Before jumping into causes, it helps to understand the basics of how your air conditioning system manages moisture.
How Air Conditioners Produce Water
Your air conditioner doesn’t just cool the air — it also removes humidity from it as part of the cooling process. As warm, moist air passes over the cold evaporator coil inside your unit, condensation forms — just like water droplets forming on a cold glass on a hot day.
That condensation drips into a collection tray (the drain pan) and flows out through a condensate drain line, safely away from your home.
When anything interrupts that drainage process — a blockage, a crack, a freeze-up — the water has nowhere to go. It backs up, overflows, and ends up dripping inside your home instead.
That’s the short version. Now let’s look at exactly what goes wrong and why.
7 Common Causes of Air Conditioner Leaking Water Inside
1. Blocked Condensate Drain Line
The Most Common Culprit in Perth Homes
This is hands-down the most frequent reason for an air conditioner dripping water inside — and Perth’s dry, dusty environment makes it even more common here than in other Australian cities.
Over time, dust, dirt, mould, algae, and debris accumulate inside the condensate drain line — the small pipe that carries water away from the indoor unit. When that line gets clogged, water has nowhere to drain. It backs up into the drain tray, which overflows, and then leaks out of the unit and onto your wall, ceiling, or floor.
Signs of a blocked condensate drain:
- Steady dripping from the indoor unit
- Water pooling directly below the wall-mounted unit
- A musty or damp smell coming from the system
- The leak gets worse the longer the unit runs
Quick Fix — Clearing a Blocked Drain Line
For minor blockages, you can try this yourself:
- Turn off the air conditioner completely at the power point
- Locate the condensate drain line (usually a small PVC pipe near the indoor unit)
- Use a wet/dry vacuum to suction out any debris from the end of the drain line
- Flush the line with a mixture of warm water and white vinegar to break down organic build-up and kill mould
- Restart the system and monitor for dripping
If the blockage is severe or the leak continues, contact a licensed Perth air conditioning technician.
2. Dirty or Clogged Air Filter
A Dirty Filter Causes More Problems Than You Think
A blocked air filter is one of the most overlooked causes of AC leaking water inside. When your filter is clogged with dust and debris, it restricts airflow across the evaporator coil. Without enough warm air flowing over it, the coil gets too cold and freezes over — turning into a block of ice.
When the system eventually warms up or is switched off, that ice melts rapidly. The sudden rush of water overwhelms the drain tray, which overflows and leaks inside your home.
In Perth’s dusty conditions — especially during summer and bushfire season — filters can clog up much faster than the manufacturer’s recommendations suggest.
Quick Fix — Clean or Replace Your Filter
- Turn off the unit and locate the air filter (usually behind the front panel of the indoor unit)
- Remove the filter and inspect it — if it’s visibly grey, clogged with dust, or hasn’t been cleaned in months, it needs attention
- Wash reusable filters under cold water, allow to dry completely, then reinsert
- Replace disposable filters with a compatible new one
- For most Perth homes, cleaning or checking filters every 4–6 weeks during peak season is good practice
3. Frozen Evaporator Coil
When Your Coil Turns to Ice
Even if your filter is clean, the evaporator coil can still freeze due to other causes — most commonly low refrigerant levels or restricted airflow from other sources. A frozen coil means your split system air conditioner is leaking water when the ice eventually melts, often in large quantities that the drain tray simply can’t handle.
Signs of a frozen evaporator coil:
- Reduced or weak airflow from the vents
- Ice visible on the indoor unit or refrigerant lines
- Water suddenly leaking after the unit has been running for a while
- The unit blowing warm air despite being set to cool
What to Do About a Frozen Coil
- Switch the unit off immediately — running it with frozen coils causes further damage
- Let it thaw completely (this may take several hours)
- Check and clean the air filter
- Check that all vents in your home are open and unobstructed
If the coil keeps freezing after you’ve checked the filter, the cause is likely low refrigerant — and that requires a licensed HVAC technician to diagnose and recharge safely.
4. Cracked or Damaged Drain Pan
When the Safety Net Has a Hole
The drain pan sits underneath your evaporator coil and catches all the condensation that drips off it. Over time — particularly in older Perth homes where air conditioning systems haven’t been serviced in years — the drain pan can corrode, crack, or become misaligned.
When that happens, water escapes from the pan before it even reaches the drain line. You’ll typically notice dripping from the bottom or sides of the indoor unit.
Quick Fix Options
- Inspect the drain pan carefully for visible cracks, rust, or discolouration
- Small cracks can sometimes be temporarily sealed with waterproof epoxy
- A severely corroded or damaged pan needs full replacement — this is a job for a professional
5. Improper Installation or Unit Not Level
A Common Problem in Perth’s Rapidly Built New Homes
If your air conditioning unit was not installed correctly — or if it has shifted slightly over time — it may not be sitting level. The indoor unit needs to be positioned at a very slight backward angle so that condensation naturally flows toward the drain outlet.
If the unit tilts the wrong way, water pools on the wrong side of the tray and spills over the edge before reaching the drain. This is particularly common with wall-mounted split systems in newer Perth homes where installation was rushed.
How to Address It
This is not a DIY fix. A licensed air conditioning technician needs to assess the installation angle and reposition the unit correctly. Attempting to adjust a wall-mounted unit yourself risks damaging the refrigerant lines and electrical connections.
6. Faulty or Failed Condensate Pump
When Gravity Alone Isn’t Enough
Some Perth homes — particularly apartments or properties where the indoor unit can’t drain by gravity alone — rely on a condensate pump to push water out of the system. If this pump fails or the float switch gets stuck, water backs up rapidly and overflows inside.
Signs of a condensate pump issue:
- The unit turns itself off unexpectedly (triggered by overflow safety switch)
- Water pools around the base of the indoor unit with no obvious drain blockage
- The leak seems intermittent, worsening when the unit runs for longer periods
A failed condensate pump is a technician job — do not attempt to repair or replace it yourself as it involves electrical components.
7. Low Refrigerant Levels
The Invisible Cause You Can’t Fix Yourself
Low refrigerant is one of those causes that sneaks up on Perth homeowners. When refrigerant drops below the correct level — usually due to a slow leak in the system — the evaporator coil runs colder than it should. This leads to freezing, and then the thaw cycle produces more water than the system can manage.
Low refrigerant also means your ducted air conditioner or split system is working harder than it should, driving up your electricity bills and putting extra wear on the compressor.
Important: Handling refrigerant in Australia requires a valid ARCtick licence. Never attempt to recharge refrigerant yourself — it’s illegal and dangerous. Always contact a certified Perth HVAC technician.
Should I Turn Off My Air Conditioner If It’s Leaking Water?
Yes — absolutely. The moment you notice your air conditioner leaking water on the floor or dripping from the indoor unit, switch it off at the wall.
Here’s why this matters:
- Water dripping near electrical components inside the unit creates a genuine safety risk
- Continuing to run a leaking system often makes the underlying problem worse
- Water damage to your ceiling, walls, or flooring can escalate quickly the longer you leave it running
- Mould can begin growing within 24–48 hours in damp conditions — particularly relevant in Perth homes that are well-sealed and insulated
Once you’ve switched it off, assess the situation calmly and work through the checklist above.
Air Conditioner Leaking Water vs Refrigerant Leak — What’s the Difference?
This is a question Perth homeowners often ask — and it’s an important one.
Water Leak
The liquid dripping is condensation — clear, odourless water. This is always the result of a drainage or airflow issue inside the system. It is not immediately dangerous but needs to be addressed promptly to avoid water damage and mould.
Refrigerant Leak
Refrigerant doesn’t typically drip as a liquid in domestic situations — it usually escapes as a gas. Signs of a refrigerant leak include:
- The system blowing warm air despite being set to cool
- Ice forming on the outdoor unit or refrigerant lines
- A faint chemical or sweet odour near the unit
- Higher than normal electricity bills
If you suspect a refrigerant leak, switch the unit off and contact a licensed technician immediately. Refrigerant gases can be harmful to your health and the environment.
Can a Leaking Air Conditioner Cause Mould in Your Perth Home?
Yes — and this is one of the most serious consequences of leaving an air conditioner water leak unaddressed.
Persistent moisture from a leaking unit creates ideal conditions for mould growth inside your walls, ceiling cavities, and around duct systems. Once mould takes hold, it can spread through your home’s air system and circulate spores throughout every room.
In Perth homes — which are well-sealed for energy efficiency — mould can become a serious indoor air quality issue that affects respiratory health, triggers allergies, and causes lasting structural damage to your property.
If you’ve had a leak running for more than a day or two, have the affected area inspected for mould once the leak is fixed.
How to Prevent Air Conditioner Water Leaks in Perth
Prevention is always easier than dealing with the aftermath of a leak. Here are the most effective steps for Perth homeowners:
Clean or Replace Air Filters Regularly
Check filters every 4–6 weeks during peak summer use. A clean filter is the single most effective thing you can do to prevent both water leaks and reduced system efficiency.
Schedule Annual Professional Servicing
A yearly service by a licensed Perth air conditioning technician covers drain line cleaning, coil inspection, refrigerant level checks, and overall system health. It’s the most reliable way to catch small problems before they become expensive ones.
Keep Drain Lines Clear
Consider having your technician install a drain line access point during servicing — this makes future cleaning and maintenance much easier and more thorough.
Don’t Block Vents or Restrict Airflow
Make sure furniture, curtains, and other objects aren’t blocking your indoor unit’s air intake or outlet vents. Restricted airflow is a leading cause of coil freezing and subsequent water leaks.
Act Quickly When You Spot the First Drip
A small drip today can become a significant water damage problem within days. Don’t put it off.
When to Call a Licensed Perth Air Conditioning Technician
Some air conditioner water leak situations are beyond DIY — and trying to fix them yourself can make things worse or create safety risks.
Call a professional immediately if:
- The leak continues after you’ve cleaned the filter and checked for obvious blockages
- You can see ice forming on the indoor unit or refrigerant lines
- Water is dripping near electrical components or power points
- You suspect a refrigerant leak
- The condensate pump needs repair or replacement
- Water staining has appeared on your ceiling — this may indicate a ducted system issue in the roof space
- The unit is making unusual noises alongside the leak
A licensed, qualified Perth HVAC technician will diagnose the root cause properly, carry out repairs safely, and ensure your system is running as it should before they leave.
Frequently Asked Questions About Air Conditioner Leaking Water
1. Why is my air conditioner leaking water inside my house?
The most common cause is a blocked condensate drain line. Dust, mould, and debris build up inside the pipe over time and stop water from draining properly. Other causes include a dirty air filter, frozen evaporator coil, cracked drain pan, or low refrigerant levels.
2. Is it normal for an air conditioner to drip water inside?
No — it is never normal. A small amount of condensation on the outdoor unit is fine, but any water dripping from your indoor unit means something in the drainage system has gone wrong and needs attention straight away.
3. Should I turn off my AC if it is leaking water?
Yes — switch it off at the wall immediately. Water near electrical components inside the unit is a safety risk. Continuing to run a leaking system also makes the problem worse and can cause serious damage to your ceiling, walls, and flooring.
4. Can a dirty filter cause my air conditioner to leak water?
Yes. A clogged filter blocks airflow over the evaporator coil, causing it to freeze. When the ice melts, it releases more water than the drain tray can handle — and the overflow leaks inside your home. Cleaning your filter every 4 to 6 weeks during summer prevents this.
5. Can a leaking air conditioner cause mould in my home?
Yes — and quickly. Persistent moisture from a leaking unit creates ideal conditions for mould growth inside walls, ceiling cavities, and duct systems. In well-sealed Perth homes, mould can begin growing within 24 to 48 hours of a leak starting.
6. How often should I service my air conditioner to prevent leaks?
Once a year is the recommended minimum for most Perth homes. A professional service covers drain line cleaning, coil inspection, refrigerant checks, and filter assessment — catching small problems before they turn into water damage.
7. When should I call a professional instead of fixing the leak myself?
Call a licensed technician straight away if the leak continues after basic checks, you see ice on the unit or pipes, water is near electrical components, the unit keeps switching off on its own, or ceiling staining has appeared. These signs point to a deeper issue that needs professional diagnosis.
Conclusion
An air conditioner leaking water inside your Perth home is one of those problems that rarely fixes itself. In most cases it starts small — a drip here, a damp patch there — and escalates quickly if left unattended.
The good news is that the majority of causes are entirely preventable with regular maintenance and prompt attention when something doesn’t look right. Keep your filters clean, get your system serviced annually, and don’t hesitate to call a professional the moment a leak goes beyond what basic checks can resolve.
Your home, your family’s health, and your air conditioning system are all worth looking after properly.