One of the most common questions we get on a hot summer here in Spain is “why is my air conditioning unit leaking water?”. You will normally find suddenly water starts dripping from the indoor unit onto the floor. Often at the most inconvenient times such as the hottest times.

First recommendation is to switch off the unit to prevent more damage to your home. But often the fault can be easily rectified.

The first thing is to recognise that water is supposed to be in the unit. This comes from the air conditioning units evaporator coil this cools the warm air that is blown over the top of it. Doing this generates condensation (moisture) that forms on the coil itself. Easiest way to describe this is how water droplets form on a cold glass on a hot summers day.

Now this water moisture should drip a drain pan and down into the condensate drain line and out of your home. But sometimes that fails and the main reasons are outlined below.

Reason 1: Clogged condensate drain line

The drain line is the pipe or hose that comes out of the unit and is the most common reason for water leaks from your AC unit.

If it becomes clogged with dust, dirt or mold you will find the water backs up into your home because it has nowhere else to go. The pipe will need unclogging to allow the waterflow to return.

Reason 2: Damaged drain pan

Before the water goes into the condensate pipe it gathers on a small pan. The problem is on older units these pans often rust and need to be replaced. As quite simply the water is dropping out the bottom of the pan because its leaking.

Reason 3: Broken condensate pump

If you are below the level of the pipework for example in the basement or cellar. There should be a condensate pump, if that fails it simply can’t pump against gravity as such causes the unit to leak water. A simple replacement of the pump should solve the issue.

Reason 4: Dirty air filter

Although you may not realise it a blocked filter restricts the air flow over the evaporator coil. As such the evaporator begins getting too cold and freezes over. As such the water produced is above what the pipework and pan can handle. So cleaning the filter can fix this issue or if in very poor condition replacing the filter.

Reason 5: Low refrigerant in system

Low refrigerant can also be an issue relating to a water leak in the air conditioning unit. As it generates low pressure in the system which causes the evaporator coil to freeze over. Which then melts excess water and the drain pan then overflows. You can normally recognise this issue if its not cooling well or you hear hissing or bubbling noises letting you know its a refrigerant leak.

Similar to a dirty air filter, low refrigerant will lower pressure in the AC system, causing the evaporator coil to freeze over. When the coil melts, water overflows the drain pan. If this happens it may be repairable or in many cases the unit could need replacement.

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