Understanding the Causes of Evaporator Coil Leaks in Your A/C and What Can Be Done

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If water has ever started pooling around your central A/C, you might wonder why and what causes it. Chances are, it’s your evaporator coil that’s causing the leak. The good news? The causes of evaporator coil leaks are 100 percent preventable. By understanding these causes and knowing what can be done about them, you can keep your home and A/C from damage.

Why Does My A/C Leak?

A big part of what your A/C does is pull humidity from the air. Your A/C unit pulls in hot, humid air, then runs it over the evaporator coil to cool the air down before recirculating it throughout your home. In doing this, water forms on the coil, just like you get condensation on any chilled surface on a hot, humid day.

This condensation then moves into a sloped drain pan so it can go down the drain line, which either connects to existing plumbing or goes outside your home. The causes of evaporator coil leaks always have to do with some part of this system, so by knowing how it works, you can prevent problems from starting.

Problems in the Drainage

The most common causes of evaporator coil leaks are a clogged drain line or a rusted condensation pan. The drain line can get clogged with all sorts of things, like insects, mold or dirt, which then means the water coming off the condensation coil has nowhere to go. It can end up backing up into your home, rather than exiting properly.

This is one of the easier problems to fix. Using a wet-dry vacuum, you can suck the blockage out of the drain line. It’s also one of the easier problems to avoid. The blockage usually comes from a dirty evaporator coil. Cleaning the coil should be part of an annual HVAC maintenance appointment, which can help you prevent bigger problems as well.

However, another cause of evaporator coil leaks is a rusted drain pan. This can also be avoided with proper maintenance. If an HVAC technician sees signs that the drain pan is rusting, they can replace it, keeping you from ever dealing with leakage in your home.

Frozen Evaporator Coils

Another major cause of evaporator coil leaks is when the evaporator coil freezes over. When the coil eventually melts, there may be too much condensate for the pan to handle, so a good portion of it ends up in your home. But why does your evaporator coil freeze over?

The answer is usually either a dirty air filter or low refrigerant. A dirty air filter blocks airflow to the evaporator coil, which then drops the temperature around it, causing it to freeze. You should remember to regularly check the air filter and change it when it’s dirty. Not only will this keep your system from leaking, but a clean air filter also helps it run more efficiently. Low refrigerant also causes the coil to become colder than usual, creating ice /steps-to-a-healthy-home-with-better-indoor-air-quality/buildup.

If your evaporator coil freezes over, turn the A/C from “auto” to “on” so the system can defrost slowly in a way that won’t overwhelm the pan. You should also call a certified HVAC technician as soon as possible to make sure no damage was done to your system when the coil froze.

Like other causes of evaporator coil leaks, these are preventable with good maintenance.

Improper Installation

If you’re dealing with a newer system and water is leaking, there’s a good chance the system was installed improperly. If the condensate trap is set up poorly, it will keep it from draining outside your home, and instead drain indoors. In this case, you’ll need to have a licensed professional look at the system and determine how to fix the condensate trap.

If you need to schedule annual A/C maintenance or have questions about a leaky unit, make sure to contact us at Air Control Heating & Cooling. We’ve been serving the greater Tallahassee area for more than 45 years.


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