Why is My AC Leaking?

An air conditioning system is supposed to keep a home cool during high temperatures outside, but it’s not supposed to be the source of a water leak in a home.

Air conditioning on the wall above the sofa cushions.

That said, because the nature of how an AC system works isn’t commonly understood, the very features one should watch out for tend to be ignored by homeowners. And that can allow a big problem to occur with possibly serious damage to a home as well, both immediate and over time.

How an AC Works

When the air around a person gets hot, the body cooling system kicks in, which we experience through perspiration. However, if the air around a person is already humid, then the perspiration has no effect. This is why it feels hotter in countries and locations where the humidity is already very high, such as in the tropics. An AC pulls the air through a filtering process that removes the moisture from it. The emitted dry air is then cooled and sent back into the home, cooling it down. Since the body can now perspire normally, the homeowner feels cool and comfortable versus the hotter temperature outside. However, all that water that the AC unit extracts has to go somewhere. Normally, the system has a collector and drain channel that aggregates the water and allows it to exit outside. This is why a person can see dripping coming from an AC unit extended from an outside wall.

Common AC Leak Causes

Leaking through the normal drainage of an AC is not a problem. This is the correct operation as the unit extracts and removes water from a home’s internal air. Leakage into the home, through the roof or wall, or onto floors is another matter entirely and should be fixed right away. The causes of AC water leaks that need to be addressed include:

The drainage doesn’t work – The drain line in an AC is not a very large pipe. Usually it’s about a half inch PVC in diameter. Over time, this can get clogged with sediment. When completely blocked, the water will back up into the AC collector and overflow.
A leak or crack in the overflow pan – Inside the AC there is a secondary defense when the collector has too much water. However, this is only a temporary protection. If too much water is aggregating, then the overflow pan will leak as well. If the pan is compromised by cracking altogether, then it fails and the water goes to the floor or surface where the AC is installed.
A dirty air cleaner – Filtering air requires a clean filter. When clogged, the AC works harder and it can trigger related problems.
The AC installation was done wrong – This is typically associated with a mistake in how the AC drainage was connected.
The AC pump no longer works right – The pump helps move air through the system and pushes the water into the drainage process. When the pump goes faulty, the water drainage doesn’t happen.

Anytime water is leaking into a home, help should be brought in to fix the problem as soon as possible. Ongoing water leakage not only creates contact damage to the surface where the water is dripping or spilling, it also creates the risk of mold and mildew settling in, which can trigger more damage and mitigation expense. Once that occurs, the repair can end up being two phases: one to remove all the damage that could be toxic, and the second to repair the leak and restore the affected home area. Remember, an AC leaking out through its normal drain system is not a problem. When a leak is happening inside a home, it's time to call for AC professional help right away!