Quick Answer
An air conditioner leaking water indoors is almost always caused by a blocked condensate drain, a dirty air filter, or a frozen evaporator coil. Most causes are DIY-fixable in 30–60 minutes for little to no cost. If you see water dripping from the indoor unit, turn the system off immediately to prevent water damage, then work through the checks below.
The Most Common Causes (in Order of Likelihood)
1. Blocked Condensate Drain Line
This is the number one cause. Every split system removes humidity from your room air, and that moisture collects in a drain tray before exiting through a small plastic drain pipe (the condensate line). In Melbourne’s humid summer conditions, algae, mould, and dust build up in this pipe over time, blocking the flow. Water backs up in the tray and overflows into your room.
How to check: Find the drain outlet on the outside of your home — typically a small PVC pipe (12–20mm diameter) on the exterior wall near the indoor unit. Hold a tissue near it while the system is running. If no water drips out during cooling mode, the drain is blocked.
DIY fix: Use a wet/dry vacuum to suction from the outside drain end, or mix 1 part white vinegar with 1 part water and pour it slowly into the drain tray (accessible by removing the front panel). Wait 30 minutes, then flush with clean water. Repeat if needed.
2. Dirty or Blocked Air Filter
A clogged air filter restricts airflow across the evaporator coil. When airflow drops, the coil gets too cold and starts to freeze. When the system cycles off, the ice melts and overwhelms the drain tray. In Melbourne’s dusty SE suburbs — particularly near Cranbourne, Pakenham, and Officer where there’s more agricultural activity — filters block faster than in city areas.
How to check: Open the front panel of the indoor unit. The filter is a flat mesh screen behind the front cover. If it’s grey, furry with dust, or you can’t see light through it, it needs cleaning.
DIY fix: Remove the filter and wash it under a tap with lukewarm water. Let it dry completely before reinstalling. Clean filters every 4–6 weeks during heavy use periods (Melbourne summer and winter).
3. Frozen Evaporator Coil
If the coil itself freezes — visible as a thick frost buildup on the metal fins behind the filter — water drips when the ice melts. Causes include: dirty filter (see above), running the system in very low temperatures (below 16°C), low refrigerant (a job for a licensed technician), or a failing fan motor.
How to check: Turn the system off. After 30 minutes, open the front panel and shine a torch at the coil. Ice or heavy frost confirms freezing.
DIY fix: Turn the system off and let it fully defrost (1–3 hours). Clean the filter. Run the fan-only mode for 30 minutes before resuming cooling. If the coil refreezes within a few hours of normal use, you likely have a refrigerant issue — call a licensed HVAC technician.
4. Disconnected or Damaged Drain Pan
The plastic drain tray under the evaporator coil can crack, warp (especially in systems over 10 years old), or become misaligned during servicing. If the tray isn’t catching condensate properly, water bypasses it entirely. This requires opening the unit beyond what most homeowners should attempt — call a technician if you suspect a damaged drain pan.
5. Improper Installation (Low Refrigerant or Incorrect Tilt)
Split system indoor units must be installed with a very slight backward tilt so water drains toward the drain outlet. If the unit is level or tilting the wrong way, water pools in the tray and spills forward. This is uncommon in newer installations but worth checking if the problem started immediately after installation or re-mounting. Also, low refrigerant causes coil icing — low refrigerant means a leak, which requires a licensed refrigeration mechanic to repair and recharge.
Troubleshooting Table
| Symptom | Most Likely Cause | DIY Fix? |
|---|---|---|
| Water drips when cooling, stops when off | Blocked condensate drain | Yes — vacuum or vinegar flush |
| Water drips after system turns off | Frozen coil defrosting | Yes — clean filter, let defrost |
| Water pours out of indoor unit suddenly | Completely blocked drain tray overflow | Yes — urgent drain clear needed |
| Ice visible on coil or pipes | Frozen coil (filter, refrigerant, or airflow) | Partial — clean filter; call tech if refreezes |
| Water leak + warm air from indoor unit | Low refrigerant (coil icing then melting) | No — licensed HVAC technician required |
| Water stains but no visible drip | Slow drain overflow or cracked tray | Partial — inspect tray; call tech for cracks |
Step-by-Step: Clearing a Blocked Condensate Drain
This is the most common fix and costs nothing but 30 minutes of your time.
- Turn the air conditioner off at the wall. Do not just use the remote — switch off at the power point or circuit breaker to prevent electrical contact with water.
- Lay towels on the floor below the indoor unit before removing any panels.
- Open the front panel by pulling it upward at the bottom edge. The filter sits behind it — remove and set aside for cleaning.
- Locate the drain tray — the white plastic tray underneath the evaporator coil. If it’s full of water, the drain is blocked.
- Find the drain outlet on the exterior wall — a small PVC or plastic pipe near the indoor unit. Attach a wet/dry vacuum to the outside end and suction for 30–60 seconds.
- Pour a 50/50 mix of white vinegar and water into the drain tray — use a small cup. This kills algae and loosens slime buildup. Wait 30 minutes, then flush with clean water.
- Confirm the drain is clear by pouring a cup of water into the tray and watching it drain within 60 seconds.
- Clean the filter (see above), let it dry, reinstall, and close the panel.
- Restart the system and monitor for 30 minutes. No more dripping means success.
When to Call a Licensed HVAC Technician
Call a professional if:
- The coil refreezes within a few hours of defrosting and cleaning the filter — this indicates low refrigerant, which requires a licensed refrigeration mechanic in Victoria
- You see physical damage to the drain tray or coil housing
- The drain line cannot be cleared with vinegar and vacuuming after two attempts
- You notice the system blowing warm air alongside the water leak — this usually means a refrigerant issue
- Water is reaching the ceiling, walls, or getting near electrical components — turn off power immediately and call a technician
Preventing Air Conditioner Water Leaks
- Clean the filter every 4–6 weeks during active use. Set a reminder — Melbourne summers are long and dusty
- Book an annual service before summer. A technician will clear the condensate drain, check refrigerant levels, and inspect the coil — total cost $150–$250 in Melbourne
- Pour a cup of diluted bleach or white vinegar into the drain tray once every 3 months to prevent algae growth
- Don’t run the system below 18°C when outdoor temperatures are also low — this dramatically increases coil icing risk
- Check the external drain outlet each season — spiders, wasps, and geckos (common in SE Melbourne’s outer suburbs) love to nest in open pipes
Local Melbourne Resources
- Bunnings — Wet/Dry Vacuums — available at Dandenong, Pakenham, Cranbourne, and Frankston stores for clearing condensate lines
- AIRAH — Find a Licensed HVAC Technician — Australian Institute of Refrigeration, Air Conditioning and Heating directory
- Energy Safe Victoria — for electrical safety concerns relating to water near electrical equipment
- Mitre 10 — Wet/Dry Vacuums — alternative to Bunnings across SE Melbourne
Frequently Asked Questions
Is it dangerous if my air conditioner is leaking water?
Water from a leaking air conditioner is generally not dangerous by itself, but it becomes a serious hazard if it reaches electrical components — power points, ceiling lights, or wiring inside the wall. Turn the system off at the circuit breaker if water is near any electrical outlet, and don’t attempt repairs until the power is confirmed off. Prolonged leaking can also cause ceiling and wall damage that attracts mould.
How much does it cost to fix a leaking air conditioner in Melbourne?
If the cause is a blocked drain or dirty filter, the fix costs nothing — just your time. A service call from an HVAC technician to clear the drain and service the unit runs $150–$250 in Melbourne. If the problem is low refrigerant (requires a recharge), expect $200–$400 depending on the refrigerant type and how much is needed. A cracked drain tray replacement adds $100–$200 labour.
Why does my air conditioner only leak on hot days?
On very hot days, your air conditioner runs longer and removes more moisture from the air, producing more condensate than usual. If the drain is partially blocked, it can keep up on mild days but overflow on peak summer days (35°C+, which is common across SE Melbourne suburbs). Clean the condensate drain at the start of summer to prevent this.
Can I run my air conditioner if it’s leaking water?
Turn it off immediately when you notice a water leak and don’t run it until you’ve identified and fixed the cause. Running it with a blocked drain will overflow the tray further, causing water damage to your ceiling, walls, and flooring. The fix is usually quick — 30 minutes for a drain clear — so it’s not worth the risk of water damage to keep running it.
How often should I clean my air conditioner filter to prevent leaks?
Every 4–6 weeks during periods of heavy use — Melbourne summers and winters. In dustier areas like Cranbourne, Pakenham, Officer, and Berwick (more agricultural and construction activity), clean monthly. A clean filter takes 5 minutes and prevents the most common cause of coil icing and subsequent water leaks.
Final Thoughts
A leaking air conditioner is rarely an emergency — but it is a signal your system needs attention. Nine times out of ten, the fix is a 30-minute drain clean and filter wash that costs nothing. Turn the unit off, work through the checks above in order, and you’ll have it sorted before the next Melbourne summer heat wave arrives.
If the coil refreezes after cleaning, or the system blows warm air alongside the leak, call a licensed HVAC technician — low refrigerant is the likely cause and requires professional repair. The earlier you catch it, the cheaper the fix.