One of the common problems in summer is a leaking indoor AC unit. It may be leaking profusely and constantly or you may find occasional puddles around your air handler. Either way, leaking AC is not something you want to be dealing with on a hot summer day. Our Maryland AC repair specialists are here today to offer you a few ideas as to why your indoor AC unit may be leaking, as well as how to fix it. But first, let’s discuss how it works!


If your HVAC system is set up properly, you should have one AC unit outside of your home that connects to another unit indoors. Your indoor unit contains the evaporator coil and can be located next to the furnace or inside an air handler. The purpose of the evaporator is to pull the warm air from your home and cool it with the cold refrigerant as the air passes over the coil.


Besides being warm, the indoor air in summer can also get rather humid. Air contains a certain degree of moisture at all times, but warm air can hold more. On contact with the cold coil, warm air condenses and releases water, which forms into drops on the coil. It’s like pouring a glass of ice water and walking outside. You will see how drops start to bead up on the glass right away.


As the drops keep forming on the evaporator coil, they will eventually start dripping, right? Thankfully, your AC unit is equipped with a drain pan and a sloped drain pipe that carries water away as the pan gets filled. Depending on your setup, this drain line may exit either outside or into your home’s plumbing.

Now that you know where water in an AC unit comes from, let’s figure out why it’s all over your basement floor!

Reason #1: Blocked Drainage Tube

If your drainage tube is blocked completely, the water will start backing up right away. However, blockages usually happen over time and are not always complete. That’s why many homeowners often discover a leak on hot, humid days when the extra humidity in the air causes excessive condensation, so the partially blocked drain can’t keep up any longer.

Why do drain pipes get blocked? There’s dust and algae, and many other reasons! Sometimes, a dirty condenser coil may be the culprit, as the dirt mixes with the water and fills the drain with gunk. That’s why it’s important not to skip seasonal maintenance of your Maryland HVAC unit. The good news is that a wet-dry vacuum can usually resolve the clogging in minutes.

Reason #2: Rusted Evaporator Drain Pan

If your unit is old or if the water drains slowly due to blocked pipes or poor installation, the evaporator drain pan may get rusted through. In this case, the water won’t even get a chance to get to the drain—it will drip right through the pan and cause a mess. Some units have an emergency overflow pan that sits underneath the primary evaporator drain pan in case it malfunctions or overflows. If you see water in the secondary pan, that’s a sign that something is wrong.

Reason #3: Frozen Evaporator Coil

When a frozen evaporator coil starts to melt, the drain often can’t keep up, which leads to a leak. There are a few things that may cause a frozen evaporator coil. The first one is a dirty air filter that restricts the air flow over the coil. Without the warm air to pass through, the coil temperature drops so low, the coil may ice over. The second common cause is low refrigerant level that also causes the temperature to drop.

Of course, these are just some of the most common causes of a leaking indoor AC unit. If you discover a leak, we recommend turning off your AC and calling your Sykesville, Maryland AC repair technician. Our pros at Cool Breeze will promptly respond to your call and conduct a thorough inspection to determine the exact cause of your problem.