Window Air Conditioner Leaking Water: 6 Immediate Fixes

The sudden realization when you see water leaking from your window air conditioner can be mind-boggling. Do you call the HVAC guy right away? It will cost you at least $200 to fix a window air conditioner leaking water inside the house. Can you fix the window AC unit leakage yourself?

The window air conditioner leaking water seems to be one of the worst window AC problems. While you’re thinking about where the water is coming from and how to stop the leakage, the water is dripping and destroying your inside wall, carpet, and furniture.

First thing first:

Don’t panic. Follow these two steps immediately:

1. Turn off the window unit. This has to be said because a lot of people ask ‘Can we use AC when water is leaking?’. In short, no, you should not use your air conditioner when water is leaking.
2. Soak up the water leakage inside the house with a towel.

You have probably done that by now. The key thing you want to know is ‘How do I fix my window AC leaking water?’. Right?

Luckily, the window AC unit leakage is the most common and easily fixable problem. Most homeowners with older AC units had to deal with window air conditioners leaking inside the house (usually frozen refrigerant coil, located near the indoor side) or leaking on the outside wall.

And, despite what your father may have told you, you don’t need to drill a hole into the condensate pan (you might hit a refrigerant line or a wire).

First, you need to check where the water is coming from. After that, you fix the leakage whatever it may be – blocked condensate drain, low refrigerant levels, or damaged condensate pan.

There are 6 causes why a window air conditioner might be leaking. We will go through all of them; one of them is bound to be troubling your unit.

Note: These are the same 6 potential window AC unit causes that every HVAC technician you might call will go through. It’s like a checklist; if it’s not blocked condensation drain, check for refrigerant levels, and so on through all 6 steps. You can check a similar air handler leaking water inside articles for mini split ACs here and an article about air conditioner spitting water indoors here (leaking is one thing, spitting water is another).

You still might call an HVAC guy, of course. But window air conditioner dripping water is usually an easy fix, and if you can probably do it yourself, why spend $200+ for an HVAC guy to do it for you, right?

Let’s start with the most common reason why a window air conditioner might be leaking water inside the house:

1. Window AC Unit Is Leaking Water Due To Condensation Drain Blockage (Most Common Cause)

In 1 out of every 3 or even 2 cases, the water is leaking from the front of the window AC unit due to blocked condensation drain. Luckily, this is the easiest leakage cause to solve.

Function of condensation drain: Every window air conditioner removes moisture from indoor air (works like a dehumidifier). Removed moisture is collected in the condensation pan, located at the bottom of the window AC unit. The condensation drain connects the overflow pan to the drainpipe and allows for normal functioning.

Cause of window AC leakage: Condensation drain is partially or permanently blocked. Everything from dirt, mold, leaves, or even dead animals like bees can clog the condensation drain. The result is water being unable to escape from the condensate pan which, in turn, creates a spillover. You will notice that spillage as water dripping (partially blocked drain) or leaking (permanent blockage) from your window unit on the inside or outside; depending on where the window AC is leaning.

How to fix condensation drain blockage: Simple. You have to remove the blockage. Open the backside of the window AC unit and try locating the condensation drain. If you see that it’s blocked, use something thin – a needle, toothpick, thin screwdriver – and release the blockage by basically inserting the thin object into the drain and wiggling it around.

In many cases, this is the only thing you have to do. Turn on the window air conditioner and check if the leakage is fixed. Even if the outdoor temperatures are very high and you have +60% relative humidity, the window AC unit at 100% capacity should drain the excess water without any problems.

2. Water Is Leaking Through A Hole In The Condensate Pan (Older Units)

If your window AC unit has been working without problems for 10+ years, and it only now starting to leak all over the place, you might have a problem with a damaged condensate pan. Older units are especially prone to this cause of water leakage.

Function of condensate pan: Condensate pan collects the water window AC unit removes from the indoor air. This pan is located at the bottom of window AC units and has a less than 2-pint capacity. Moisture gathered there is transferred to the drainpipe via the condensation drain in a normally functioning unit.

Cause of window air conditioner leakage: Condensate pan has to be intact. If you have a hole in it or any small dent, the water will start leaking from that hole. Causes of pan damage include an unfortunate puncture being created during installation for newer units, and rusting and corrosion with older 10+ old units that have been working just fine before.

How to fix damaged condensate pan: There is no way around this; the hole or dent in the pan has to be eliminated. If can buy a new condensate pan; in all fairness, they are rather cheap (below $30). But if you want to stop the window air conditioner leakage yourself, you can use water-resistant glue or resin to close that gap in the bottom of the window AC unit.

If you have an older unit and the cause of the condensate pan is due to corrosion, you might have to close more than one gas in the pan. Chances are that new holes will form (progressive corrosion) and you will have to fix this leaking window AC problem several times.

In such cases, buying a new pan or even a new unit might be a better option. As always, make sure you buy a window AC with a high EER rating; you will find the most energy-efficient window AC unit options here.

3. Frozen Evaporator Coil Causes The Window AC Unit To Leak (Due To Dirty Air Filters)

There is a good reason why you should clean the air filters at least twice a year. Before you know it, dirty air filters can cause a frozen evaporator coil. In turn, this will cause the window air conditioner to leak, and even blow hot air (instead of cold air).

Function of air filters: As all filters, filters in the window AC are there to remove larger particles like hair, dust, bugs, and so on. As we’ve learned before, all these impurities can cause condensation drain leakage. If air filters are properly and regularly cleaned or changed, the window AC unit will receive unrestricted airflow and function normally.

How dirty air filters can lead to leakage: If air filters are not cleaned, the airflow over the refrigerant coil will be restricted (even up to 10% lower CFM might be problematic). The refrigerant coil is cold; its function is to decrease the temperature of incoming hot air. If it received less hot air than expected (due to the air filter’s restricting airflow), it will get increasingly colder, and can eventually freeze over. When that ice is melting, it can release up to 1 pint of water, and you will notice your window AC unit leaking.

How to fix dirty air filters (not as easy as it sounds): It should be as simple as ‘change the filters’, right? If you already have leakage, the refrigerant coil is probably still frozen. Changing the air filter will solve the leakage in few running hours, but be prepared with your towel! The remaining ice melting will be leaking through the window air conditioner during that time. To avoid furniture, wall, or carpet damage, make sure to be near the unit until the coil is fully unfrozen and the unit stops leaking.

A frozen evaporator coil might cause serious problems. Leakage is just the start of it; if you have been neglecting the window air conditioner leaking for some time now, other window AC problems might occur in the future. Just be vigilant and keep an eye on the unit even when you solve the leakage problem.

4. Too Low Refrigerant Levels Will Similarly Cause The Coil Freezing-Melting Leakage

Of all the causes of water coming out of the window air conditioner, the low refrigerant levels are the worst. You can fix the small leakage quite easily in a similar way as with air filters. The larger issue you will have to deal with is replenishing the refrigerant levels. You can learn more about how to recharge the freon in the window AC unit here.

Function of refrigerant: Refrigerant is the key to how air conditioners work. Expanding and compressing (that’s why the compressor is for) this fluid generates the necessary heat transfer as per the 2nd Law of Thermodynamics that facilitates the air conditioning system.

Water leakage due to low refrigerant levels: With lowering the refrigerant levels, the pressure inside the refrigerant lines will drop. This will reduce the heat transfer the window air conditioner is normally capable of. Through a cascade of reactions, the refrigerant lines will become too cold and will eventually freeze over. When they melt, you will see the window air conditioner leaking water inside the house (refrigerant coil is located near the indoor side of window AC).

How to fix the low refrigerant levels: This may sound a daunting task but with some technical skills you can put the freon in the refrigerant lines yourself. Just follow the article mentioned above, or call an HVAC technician to help you out. Just be mindful that when you refill the freon and the unit is working properly again, the remaining ice around the cold coil might melt, and you want to be ready with a towel when the water starts dripping down the inside wall.

If you need to contact HVAC support, you can use this form here to get 4 free quotes by certified and vetted HVAC technicians.

5. Condensate Pump Is Not Pumping The Water Out Properly (Basement-Level AC Units)

This is only for homeowners with below-ground level window AC units with condensate pumps. It’s one of the rarest causes of indoor window AC unit water leakage; most people can skip it but if you have this exact setup, this information might be invaluable to you.

Function of condensate pump: If you have a below-ground level AC, you will usually get an in-built pump with your AC unit. That pump is used instead of the drainpipe; it actively pumps the gathered water against gravity to the surface for proper drainage.

Water leakage due to condensate pump: Simple enough to understand. If the pump isn’t pumping the excess water to the surface, the condensate pan will quickly be overfilled and you will see a leakage.

How to fix a broken condensate pump: This is probably the one thing you can’t DIY. Built-in pumps should usually be inspected by HVAC specialists. Every unit is different and has a specific built-in pump that, when broken, causes water spillage.

An HVAC specialist will probably tell you that you have to replace the condensate pump to prevent the water from leaking all over your basement. Given these are built-in pumps, that’s not an easy task.

6. Water Leakage After Window AC Unit Installation

If you have just installed a new window air conditioner and it started leaking right away, something is probably wrong with the installation. There are several potential causes for leakage, and the leakage just might be the most apparent sign of improper installation.

Keep in mind that this may also apply if you just relocated an existing air conditioner on another window.

In every case, if you experience a window air conditioner leaking water outside or inside the house, it’s best to redo the whole installation process.

If the leakage keeps repeating after a new installation, the wisest thing is to pick up a phone and call an HVAC installation expert.

Rounding Up Ways How To Fix A Leaking Window Air Conditioner

These 6 causes will solve 90% of leakage problems. Keep in mind that water leaking from within the window air conditioner might be a sign of bigger problems.

If you see that the condensation drain is blocked or that you have a frozen refrigeration coil, you can just fix it and that’s that.

If the water still keeps leaking after the fix, you should check for other causes of leakage.

In the worst-case scenario – if you can’t DIY window air conditioner leaking fix – you can just call an HVAC repair guy and swallow that $200+ bullet.