Why Is My Aircon Leaking Water?

Why air conditioners produce water

As warm, humid air passes over the indoor unit's cold evaporator coil, moisture condenses out of the air — the same process you see on a cold glass on a humid day. This condensate is collected in a drain tray inside the unit and directed out through a condensate drain pipe.

A healthy system produces quite a lot of water in humid conditions — it is normal. The problem is when that water does not drain away as it should and ends up dripping from the front or sides of the indoor unit.

Blocked condensate drain

The most common cause of a water leak is a blocked condensate drain line. Algae, mould, dust and debris accumulate in the drain over time and eventually block the flow. Water backs up in the drain tray and overflows.

Regular servicing — which includes flushing the condensate drain — prevents this. A blocked drain can usually be cleared with a wet/dry vacuum or by blowing compressed air through the line from the drain point outside.

Dirty evaporator coil

A coil caked in dust and debris restricts airflow over the coil. This causes the coil to get excessively cold and ice up. When the ice melts — either when the unit is switched off or when defrost runs — it produces more water than the drain tray can handle quickly.

The solution is cleaning the coil. This should be done as part of a routine service.

Low refrigerant

Low refrigerant causes the evaporator pressure to drop below normal. This makes the coil colder than designed, which again leads to icing. A leaking refrigerant system should be repaired and properly regassed — topping up without finding the leak is a temporary fix.

If icing is occurring, do not continue running the unit for extended periods. Switch it off and have it assessed.

Incorrect installation

The indoor unit must be installed with a slight slope toward the drain outlet so water flows out by gravity. A unit installed level or sloping the wrong way will accumulate water in the tray and overflow regardless of how clean the drain is.

Installation errors of this kind are also why using qualified, experienced installers matters.

• ✓ Unit must slope toward the drain side
• ✓ Drain line must not have sags that trap water
• ✓ Condensate pump required where gravity drainage is not possible

When to call a technician

If cleaning the filter does not stop the leak, or if the unit is icing up, contact a technician. A water leak left untreated can stain ceilings, damage plaster, and eventually cause the drain tray to overflow into the unit's electronics.