Air Conditioner Leaking Water? Causes & Fixes
Air conditioners pull moisture out of the air as they cool, so some water is normal — it should run safely outside through a condensate drain. When water appears indoors, a drain is blocked or the coil has frozen.
A leak left unfixed can damage ceilings, floors and electrics, so tackle it promptly using the steps below.
Common causes
Blocked condensate drain
Dust and algae block the drain line so condensate backs up and overflows the tray. This is the most common leak cause.
Frozen evaporator coil
A dirty filter or low refrigerant lets the indoor coil freeze. When it thaws, meltwater overwhelms the tray and drips indoors.
Tilted or unlevel portable unit
Portable units must sit level so condensate flows to the internal tank. A tilted unit leaks from the back.
Cracked or disconnected drain pipe
A split system’s external condensate pipe can crack, freeze and split, or come loose at a joint — common after winter.
Full internal tank (portable)
Some portables store water in a tank that must be emptied; a full tank triggers a leak or an auto-shutoff.
How to fix it
- 1Turn the unit off at the wall to stop the leak immediately.
- 2For a split system, check the outdoor condensate pipe for blockages and clear it with a thin brush or wet/dry vacuum.
- 3Clean the indoor air filter — a frozen coil usually means poor airflow.
- 4Level a portable unit and empty its internal water tank if it has one.
- 5Run the unit again and watch for dripping over the next 30 minutes.
- 6If water still appears, the drain is likely cracked or the coil is frozen from low refrigerant — call an engineer.
When to call a pro: If clearing the drain and filter doesn’t stop the leak, you may have a split condensate pipe or a frozen coil caused by a refrigerant leak. Both need a qualified engineer.
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Frequently asked
Is a leaking air conditioner dangerous?
The water itself isn’t, but it can damage ceilings, floors and nearby electrics. Switch the unit off and fix the cause promptly.
Why does my portable AC leak from the back?
Usually because it isn’t level, so condensate runs away from the internal tank instead of into it. Set it level and empty the tank.
Why is my split system leaking inside in winter?
The outdoor condensate pipe can freeze and split overnight. Lagging the pipe and fitting a trace heater prevents it — an engineer can do both.