Troubleshooting Guide
Air Conditioner Leaking Water From Outdoor Unit
An air conditioner leaking water from outdoor unit panels or its base is one of the usual things owners ask about, and most of the time it is completely normal. Reverse cycle systems make water as part of their everyday work, in both heating and cooling. This guide explains how to tell harmless drips from a real fault, what you can safely check yourself, and when a licensed technician should take a look.
The Short Answer
Is Water Dripping From the Outdoor Unit Normal?
In most cases, yes. A split system or ducted outdoor unit moves heat by changing the temperature of a refrigerant coil. Whenever that coil runs colder than the surrounding air, moisture condenses on it. That water has to go somewhere, and on the outdoor side it simply drips out of the base.
However, not every puddle is innocent. A leak that appears suddenly, smells unusual, comes with ice that never clears, or arrives with a loss of heating or cooling can point to something that needs attention. The trick is knowing which pattern you are looking at.
Before reading on, it helps to note three things. First, which mode was the system running in. Second, what the weather was doing. Third, whether the water is clear and the unit is still performing well. Those clues answer most questions on their own.
All Troubleshooting Guides
Browse other common symptoms, from strange noises to weak airflow, explained in plain language.
Indoor Unit Leaking
If water is coming from the indoor head on the wall instead, our indoor leak guide covers that problem.
Ice on the Outdoor Unit
Frost and ice on the outdoor coil are closely linked to winter dripping. Read how defrost works.
Heating Mode
Why Does the Outdoor Unit Leak Water in Winter?
When a reverse cycle system heats your home, the roles of the two coils swap over. The outdoor coil becomes the cold side. It pulls warmth out of the outside air, even on a chilly morning, and pumps that warmth indoors. Because the outdoor coil is now colder than the air around it, moisture forms on its fins.
On a mild, damp day that moisture simply runs off as water. On a cold, humid morning it can freeze into a layer of frost. Frost blocks airflow, so the system runs a defrost cycle to melt it. During defrost, the unit briefly reverses, warms the outdoor coil and sheds the ice as a rush of water. Owners often notice a steady trickle, or even a small stream, from under the unit at this time.
You may also see a cloud of steam rising off the outdoor unit and hear a whoosh as the refrigerant valve changes direction. Indoors, the fan usually slows or stops for several minutes. All of this is expected behaviour. Once defrost finishes, heating resumes and the dripping tapers off.
How Much Water Is Normal in Heating?
The amount depends on the outdoor humidity, the air temperature and how hard the system is working. A large ducted outdoor unit running all evening in a damp Melbourne winter can release a surprising volume. A small bedroom split on a dry Adelaide night may barely leave a damp patch. Neither is a fault on its own.
Cooling Mode
Why Is There Water Near the Outdoor Unit in Summer?
In cooling, the indoor coil is the cold side, so the indoor unit collects the condensate. That water drains away through a flexible drain hose. On many split systems, the installer runs this hose down the wall beside the pipework, and it ends near the outdoor unit or into a garden bed close by.
As a result, a puddle beside the outdoor unit during a humid Brisbane or Sydney afternoon is often just indoor condensate leaving the house as designed. Follow the small hose from the wall and you will usually find the source. A steady drip while the system cools is a sign the drain is working, not failing.
Meanwhile, the outdoor unit itself rarely produces much water in cooling mode, because its coil runs hot. If the outdoor casing is wet in summer with no drain hose nearby, look for other reasons, such as rain, a sprinkler, a gutter overflowing above the unit, or condensation running from a roof cavity unit.
Normal or Not
How Can You Tell a Normal Drip From a Fault?
Comparing the two side by side makes the difference clearer. Use the lists below as a quick guide, then read the causes section for more detail.
Usually Normal
- Water dripping from the base during heating on a cool, damp day
- A rush of water and steam during a short defrost cycle
- Clear water from the indoor drain hose during cooling
- Light frost that melts away every so often
- Puddles that dry up once the weather warms
- Normal heating or cooling performance throughout
Worth Investigating
- Thick ice that builds up and never fully clears
- Water pooling against the house wall or under the slab edge
- Oily residue or staining on pipe joints
- Heating or cooling noticeably weaker than usual
- A flashing light or error code on the indoor unit
- Ice forming on the thin copper pipe or valves
If your situation sits mostly in the left column, there is usually nothing to fix. When symptoms from the right column appear, it is worth working through the safe checks below.
Causes
What Causes an Outdoor Unit to Leak Water?
The causes below are ranked from the simplest and most harmless to the more serious. Many homes will find their answer near the top of the list.
Normal Heating Condensate
The outdoor coil runs cold in heat mode, so water forms and drips out. This is a very frequent reason for a wet outdoor unit across all brands and all cities.
Defrost Meltwater
Periodic defrost cycles melt frost from the coil in a short burst. The water volume can look alarming, but it is the system protecting its own efficiency.
Indoor Drain Hose Outlet
The indoor unit’s condensate hose often finishes near the outdoor unit. Water here in cooling or dry mode is normal drainage from inside the home.
Blocked Base Drain Holes
Outdoor units have small drain holes in the base tray. Leaves, mud, spider nests or a unit sitting too low can block them. Water then pools in the tray, overflows in odd places, or freezes inside the unit in cold weather.
Poor Unit Position
A unit mounted flat on the ground, or tilted the wrong way, can send water against the house wall. Over time this can stain render, rot timber or wet a subfloor.
Heavy or Persistent Icing
If the coil keeps icing up and defrost never quite clears it, far more water is produced and the unit struggles to heat. This can point to low refrigerant, a faulty sensor, an outdoor fan problem or a defrost control fault.
Refrigerant Leak Signs
Refrigerant itself evaporates and does not drip like water. However, a leak often leaves an oily film at a joint, and low charge can make a pipe or valve frost over. Both need a licensed technician.
By Brand
How Do Different Brands Show Defrost and Drainage?
Every reverse cycle system defrosts, but brands signal it differently. Knowing what your unit normally does makes it easier to spot a change.
Daikin
Daikin split systems, such as the Cora, Alira X and Zena ranges, pause the indoor fan during defrost and restart once the coil is warm. The outdoor unit may steam and drip heavily for a few minutes. See our Daikin air conditioning page for more about the range.
Mitsubishi Electric
MSZ-AP and MSZ-EF wall splits stop blowing warm air during defrost. Ducted and ceiling cassette systems with a wired controller often display a defrost or standby message while it runs.
Panasonic
Many Panasonic models blink the power indicator during defrost and when warming up in heat mode. Water from the outdoor base is normal while this happens.
Samsung
Samsung systems, including WindFree models, halt indoor airflow while the outdoor coil defrosts. App users may notice the unit reporting as running with no warm air for a short time.
Fujitsu
Fujitsu Lifestyle and other wall splits stop the indoor fan during defrost. Fujitsu outdoor units commonly shed a noticeable amount of water from the base in damp winter weather.
LG and Actron
LG Dualcool and Artcool models pause heating during defrost in the same way. Actron ducted systems behave similarly, and the large outdoor coil can release a lot of meltwater in one go.
If a unit shows a fault code alongside heavy icing or leaking, note it down. Our air conditioner error codes guide explains how to read codes for each brand. For example, an outdoor coil sensor fault such as Fujitsu 73 or Actron E7 can affect how well defrost works.
Owner Checks
What Can You Safely Check Yourself?
These checks are safe for any homeowner. They do not involve opening sealed panels, touching electrical parts or handling refrigerant. If something looks wrong, stop and call a professional.
Note the Mode and Weather
Was the system heating on a cool, damp day, or cooling on a humid one? Write it down, as it explains most leaks straight away.Find the Indoor Drain Hose
Trace the thin flexible hose from the indoor unit down the wall. If it ends beside the outdoor unit, that is likely your water source.Clear Around the Outdoor Unit
Remove leaves, weeds and garden clutter from around and under the unit. Keep a clear space so air flows freely and water can escape.Look at the Base Drain Holes
From the outside only, check that holes in the base tray are not packed with debris. Gently clear visible leaves with a gloved hand or soft brush.Watch a Defrost Cycle
If you see steam, hear a whoosh and the indoor fan stops for a short while, that is defrost. Heating should return on its own.Clean the Indoor Filters
Dirty filters reduce airflow and make the whole system work harder. Wash them in lukewarm water, dry them in the shade and refit.Power Cycle if There Is a Code
Switch the system off at the isolator or breaker for a few minutes, then restore power. If the code comes back, book a technician.
Never pour hot water on an iced coil, chip ice off with tools, or spray water into the electrical side of the unit. Those actions can bend fins, damage components or create a shock risk. For general reset steps, see how to reset common air conditioning faults yourself.
Australian Conditions
Does the Weather in Your City Affect Outdoor Unit Leaks?
It does, quite a lot. Australia’s major cities have very different winters and summers, so the same unit will drip differently depending on where it lives.
Melbourne has long, cool and often damp winters. Reverse cycle systems there spend many hours heating in conditions that suit frost, so defrost water is a regular sight from late autumn through spring. Adelaide’s winter mornings can be crisp with light frost, especially in the Hills, which brings the same pattern on cold nights.
In Sydney, inland and western suburbs such as Penrith and the Blue Mountains foothills get noticeably colder nights than the coast. Units there defrost more often than those near the beaches. Brisbane winters are mild, so heavy defrost is less common, but its humid summers make indoor drain hose water near the outdoor unit very normal.
Perth sits in between. Its winters are cooler and wetter than many expect, while summers are hot and dry. Most outdoor unit water in Perth comes from heating condensate on cold mornings, or from rain. Coastal homes in every city also face salt air, which can corrode base trays and drain fittings over time and lead to leaks in unexpected places.
Technician Visit
What Does a Licensed Technician Check?
If the leak does not match normal behaviour, a technician will look at the whole system rather than just the puddle. Here is what a typical inspection covers.
- Confirming whether the water is condensate, meltwater or something else
- Checking the outdoor base tray, drain holes and any fitted drain spout
- Inspecting the indoor drain line, its fall and its outlet point
- Measuring system pressures and temperatures to confirm correct refrigerant charge
- Testing defrost operation and the sensors that control it
- Checking the outdoor fan motor and coil condition
- Looking for oil stains or corrosion that point to a refrigerant leak
- Reviewing unit mounting, level and clearance from walls and fences
- Reading any stored fault codes from the controller or board
Refrigerant work in Australia requires an ARCtick licensed technician. The technicians we send hold the licences their work requires, so leak testing, repairs and regassing are handled correctly. If you are in a capital city, start with your local page: Sydney air conditioner repairs, Melbourne air conditioner repairs, Brisbane air conditioner repairs, Perth air conditioner repairs or Adelaide air conditioner repairs.
Safety
Is It Safe to Keep Running the System?
If the water is from normal condensate or defrost, there is no reason to stop using the air conditioner. It is doing exactly what it was designed to do. Simply keep the area around the outdoor unit tidy so water can drain away.
On the other hand, switch the system off and book an inspection if ice keeps building up, heating is poor, a fault code appears, or you smell burning. Running a heavily iced unit for long periods can strain the compressor and fan. Similarly, water pooling against a wall or near a power point should be dealt with promptly.
Open more detail
Some owners worry that dripping wastes energy. In reality, condensate and defrost are part of normal heat transfer. What does waste energy is a coil that stays blocked with ice or dirt, because the system then runs longer to reach the set temperature.
If the water is damaging paving, timber decking or a garden bed, a technician can often fit a drain spout to the outdoor base and pipe the water to a better spot. Raising the unit on proper feet or a bracket can also help in frost-prone areas, since it stops meltwater refreezing around the base.
Finally, remember that rain can make an outdoor unit look like it is leaking. Check whether the casing is wet on top as well as underneath before assuming the water came from inside.
Questions
Frequently Asked Questions
Why is my outdoor unit leaking water when heating?
In heat mode the outdoor coil runs cold, so moisture from the air condenses on it and drips out. Defrost cycles add extra meltwater. Both are normal.
Is steam from the outdoor unit a problem?
No. Steam usually means the unit is in defrost and melting frost off the coil. It should stop within several minutes as heating resumes.
Should the outdoor unit drip in cooling mode?
The outdoor unit itself rarely drips in cooling. Water nearby is usually from the indoor drain hose, which often ends beside the outdoor unit.
Can I redirect the water away from my wall?
Often, yes. A technician can fit a drain spout to the base tray and run a hose to a garden bed or drain, or raise the unit on feet.
Does leaking water mean low refrigerant?
Not usually. Refrigerant is a gas and does not drip. However, heavy ice that never clears can be linked to low charge, which a licensed technician should check.
How often does a defrost cycle run?
It depends on the weather. On cold, damp days defrost may run fairly often, while on mild, dry days it may hardly run at all.
Can a blocked drain hole damage the unit?
It can. Water trapped in the base tray can freeze around the fan or coil in cold weather and may encourage corrosion over time.
Related Help
Where Can You Find Related Guides?
These pages cover nearby problems and local services. You can also return to our main page for air conditioning service Australia wide.
Still Unsure About the Water Under Your Unit?
Describe what you are seeing and we will arrange a licensed technician to check it.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles