Window AC Leaking Water? Here’s What to Do

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Is water leaking out of your window AC and into your home? Water leaking from a window AC is a serious problem. Major damage can occur if you don’t act fast

The first thing you should do is turn off your window AC. Next, get a towel and soak up the water so it doesn’t damage your home.

Okay, so now that that’s done, it’s time to start figuring out what your next steps are.

In this article, I’ll go over what you need to do if your window air conditioner is leaking water. I’ll also provide step-by-step instructions for troubleshooting a leaky air conditioner in any situation.

Check if the condensate drain is clogged

In most cases, if a window AC is leaking water inside, then it’s due to a clogged condensate drain. So the first thing that you should check is if the condensate drain is plugged.

What’s the condensate drain used for?

All ACs produce water when they cool the air. The reason is that cold air holds less moisture than warm air. So when the AC cools warm moist air, some of that moisture comes out of the air and turns to liquid.

As the AC runs, the liquid condensate collects in a drain pan. The condensate drain is a hole in the drain pan that allows excess water to drip out of the back of the window AC. If the hole gets clogged, then there is a possibility that the drain pan will overflow and start leaking water in your house.

Why does the condensate drain get clogged?

The condensate drain can get clogged from all sorts of things:

  • Dirt
  • Mold
  • Slime build-up
  • Leaves
  • Dead animals or insects
  • Rust

Keep in mind that a clogged condensate drain won’t always cause your window AC to leak water. Most newer window AC models are the dripless type. This means that they won’t normally drip out water from the back of the unit.

How to fix a clogged condensate drain on a window AC

To fix a clogged window AC condensate drain, follow these steps:

  1. Unplug the window AC from the power outlet. If you’re going to be unclogging your window AC’s drain, remove its power source.

  2. Find the condensate drain. The condensate drain is located somewhere on the back of the window AC. Go outside and look for the drain hole. Take note of how large the hole is, you’ll need to find a tool that is the right size to clean it out.

  3. Unclog the condensate drain. Use a thin tool such as a needle or paperclip to poke inside of the condensate drain and dislodge the debris. You may be able to use a thin screwdriver if the drain hole is big enough. In most cases, this is enough to unclog the drain and get all the excess water out of the drain pan.

After you unclog the condensate drain, go ahead and plug the AC back in and turn it on to test its operation.

If the condensate drain gets clogged again, you may need to open up the window AC and clean its drip pan out.

Check if evaporator coil is frozen

The evaporator coil is the part of the window AC that gets cold. In some cases, the evaporator coil will get excessively cold and a block of ice will form over the coil.

Once an evaporator coil freezes, there is a good chance that the window AC will start leaking water.

Why does a frozen evaporator coil cause a window AC to leak water?

A frozen evaporator coil is essentially a big block of ice on your window AC. As the ice melts, water starts dripping off the evaporator coil. Usually, the drip pan is able to catch all the water drops. However, if the coil is excessively frozen, water may start dripping out of the front of the window AC unit.

What causes a frozen evaporator coil?

If your window AC’s evaporator coil is freezing, then that is a bad thing—for many reasons.

  1. Your window AC won’t produce enough airflow since the ice is in the way.
  2. You window AC might start leaking water when the ice melts.
  3. A frozen evaporator coil is indicative of another issue, such as low airflow or low refrigerant.

How to fix a frozen evaporator coil

If your window AC’s evaporator coil freezes, then you have a bigger issue on your hand. Most likely it’s an airflow issue.

The first thing you should check is the air filter. Make sure that the air filter is clean. If the air filter is dirty, then clean it.

A clean air filter keeps air flowing through your window AC. A dirty air filter will inhibit airflow and potentially cause a frozen coil.

Once you get sufficient airflow flowing through your window AC unit, the evaporator coil shouldn’t freeze anymore. If it’s still freezing, then it’s likely that the AC is low on refrigerant.

Under normal operation, air conditioners don’t “use up” refrigerants. So if your AC is low on refrigerant, that means that there is a refrigerant leak somewhere.

Unfortunately, if your window AC has a refrigerant leak, you’re often better off replacing the entire unit rather than trying to get it fixed. It’s often cheaper to just buy a new one instead.

Check if the air filter is dirty

The air filter is the part of the AC that captures particles. There are two reasons why an air filter is important:

  1. The air filter captures particles so the air conditioner’s internal components don’t get dirty.
  2. The air filter captures particles to keep them out of the air in your room.

Why does a dirty air filter cause a window AC to leak water?

If the air filter gets dirty, there will be a reduction in airflow through your window AC. A dirty air filter will potentially cause the evaporator coil to freeze over. As the evaporator coil thaws out, water may leak from the front of the AC into your home.

What causes a dirty window AC air filter?

A dirty air filter in your window AC is nothing to be afraid of. In fact, it’s completely normal to have some dust accumulated on your AC’s air filter.

As your window AC runs, it sucks in air from your room, through the air filter, and into the AC. As air flows through the air filter, small particles such as dust, hair, and pollen get trapped in the air filter.

Fortunately, the air filters in most window ACs are reusable, so they can be cleaned and used again.

How to clean a window AC air filter

Cleaning the air filter in a window AC is a simple task that you should do once a month. To clean the air filter in your window AC, you need to remove the front panel to access the air filter. Next, remove the air filter from the filter slot.

After you get the filter out of the AC, clean the filter by rinsing it out with water. You can use a soft-tipped nylon brush and soap to scrub the filter if more cleaning is needed.

I have another article that has step-by-step instructions on how to clean a window AC air filter.

Check if the refrigerant is low

The refrigerant is the fluid inside of the AC that moves heat from the inside of your room to the outside of your house.

Low refrigerant levels may cause a window AC to start leaking water.

Why does low refrigerant cause a window AC to leak water?

If the refrigerant is low inside your window AC, then the evaporator coil may freeze up into an ice block. Once this happens, your window AC may start leaking water as the ice block thaws out.

What causes low refrigerant in a window AC?

In normal circumstances, refrigerant won’t leak out or get “used up” in an air conditioner. The refrigerant is inside the window AC in a “closed-loop” system so it should never come into contact with the outside world.

However, refrigerant may sometimes leak out of a malfunctioning AC. For instance, if one of the refrigerant pipes in your AC cracks, the refrigerant will leak out. Also, refrigerant may leak out of a corroding evaporator coil.

What to do if your window AC is low on refrigerant

If your window AC is low on refrigerant, you have two options:

  1. Hire a licensed HVAC professional to fix the leak and refill your window AC with refrigerant.
  2. Replace the entire window AC unit.

Of these two options, it’s often cheaper to replace the entire window AC unit. Especially if it’s a small one.

Hiring an HVAC professional to fix your window AC may seem like the smarter route, but the costs of labor are often too high when compared to just buying a brand new AC.

The only time I would recommend hiring an HVAC professional to fix a window AC is if it is a large, expensive window AC unit.

Check if the condensate pump is working

The condensate pump is a device that moves liquid condensate from your window AC up and out of your home. A condensate pump is required if your window AC is located at a lower elevation than the place that you want to drain it at.

For example, condensate pumps are typically found in basements. Since the basement is below ground level, a condensate pump is needed to pump the condensate up and outside the house.

Why does a broken condensate pump cause a window AC to leak water?

If your window AC uses a condensate pump, then the AC will collect excessive amounts of water if the pump is not working.

As the AC runs, condensate collects in the AC’s drain pan. If the drain pan fills up with water, water will start to leak out of the window AC.

What causes a broken condensate pump in a window AC?

An air conditioner’s condensate pump may break due to one of a few things:

  • Mineral deposit accumulation on pump’s parts
  • Grime build-up inside the pump’s internal components
  • Worn out mechanical or electrical components in pump

In any case, it’s often easier to replace the condensate pump than to try and get a broken one working again.

If you want to try to troubleshoot a broken condensate pump, then you should start by inspecting the float switch and cleaning the pump out.

Window AC leaking water inside when it rains

If your window AC is leaking water inside your home when it rains, then you need to check two things:

  1. Check if the window AC is sloped down toward the outside so it drains outside when it collects water.
  2. Check if the seal around the window unit is intact so water can’t infiltrate the AC unit.

Window AC needs proper slope when installed

If it rains outside, rain water may collect inside the AC’s drip pan. If your window AC is not sloped downward toward the outside, then that rain water may end up leaking inside your house.

To make sure that doesn’t happen, ensure that your window AC is installed with the proper slope. Also, make sure that the window AC’s drain pan is clear and the drain hole is open.

Window AC needs a seal around the unit

If your window AC is leaking around the perimeter of the unit inside your home, then the seal around the AC unit may not be working. 

Inspect the seal and barrier around the window AC to ensure that there are no gaps that would allow rainwater to get inside your home.

If you find a gap, you can use a piece of foam tape or aluminum tape to block the gap—depending on how big the gap is.

Window AC leaking water outside

Water leaking out of the part of the window AC that is outside is normal in most cases. So there is no need to be alarmed.

Even “dripless” window AC units will sometimes “leak” water out of the back during humid days. This is normal behavior and indicates that your window AC is doing it’s job at cooling and dehumidifying your home’s air.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

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