Air Conditioner Leaking Water? Why & What to Do

air conditioner leaking water

Air conditioner (AC) units leaking water can be a worrisome issue for homeowners. Understanding the reasons behind this problem and knowing how to address it is essential for maintaining the AC’s efficiency and preventing potential damage to your home. Here’s a summary of why an air conditioner might be leaking water and what you can do about it:


  • Condensation: The most common reason for an AC unit leaking water is condensation. As warm indoor air passes over the cold evaporator coils inside the AC, moisture in the air condenses into water droplets. This condensate is usually collected in a drain pan and then drained away. Problems with this drainage process, such as a clogged drain line or a damaged drain pan, can lead to water leakage.
  • Clogged Drain Line: Over time, the drain line that carries away the condensate can become clogged with dirt, debris, or algae. This blockage restricts water flow, causing it to back up and eventually leak from the AC unit.
  • Frozen Evaporator Coils: If the AC runs continuously, has a refrigerant leak, or experiences other issues, the evaporator coils can freeze. When they thaw, the excess water may overflow the drain pan, leading to leakage.

What to Do

  • Turn Off the AC: If you notice water leaking from your AC unit, the first step is to turn off the AC system. Continuing to use it can exacerbate the issue and potentially cause more damage.
  • Check for Blockages: Inspect the drain line and drain pan for clogs or blockages. Clear any obstructions you find. This may require using a wet/dry vacuum or a pipe cleaner to remove debris.
  • Clean or Replace Air Filters: Dirty or clogged air filters can restrict airflow, leading to increased condensation. Regularly clean or replace your air filters to ensure proper airflow and reduce the risk of water leakage.
  • Schedule Professional Maintenance: Consider scheduling routine maintenance with a professional HVAC technician. They can inspect your AC system, clean coils, and ensure all components are in good working order. Regular maintenance can prevent water leakage issues and extend the lifespan of your AC unit.
  • Check for Refrigerant Leaks: If you suspect a refrigerant leak is causing frozen coils, contact a professional technician to diagnose and repair the issue. Refrigerant leaks should be addressed promptly to prevent further damage to your AC system.

Where Does the Water Leaking From an AC Come From?

To understand why your air conditioner is leaking water, I believe it is important to first understand how your air conditioner works.

Air conditioners have 4 main parts. These are the evaporator coil, compressor, condenser coil and expansion valve.

The evaporator coil is the indoor unit while the compressor and condenser coil form the outdoor unit. A chemical with a low boiling point and high latent heat called a refrigerant is circulated between the 4 AC components using copper tubes.

The refrigerant absorbs heat from the indoor air inside the evaporator coil and releases it to the outside inside the condenser coil. Both evaporator and condenser coils have fans to help fasten the heat exchange process.

The function of the compressor is to compress the refrigerant (in gas state) so that its temperature can increase relative to the outside summer temperature. The temperature differential allows the refrigerant to lose heat to the surrounding air.

After condensation inside the condenser coil, the expansion valve lowers the pressure and therefore temperature of the refrigerant by forcing it through a small opening.

I will focus more on the evaporator coil since that is usually the source of the water that air conditioners leak.

You see, apart from temperature regulation, the air conditioner is also designed to remove humidity from your indoor air. Both cooling and dehumidification happen on the surface of the evaporator coil.

When the AC unit is turned on, the evaporator fan pulls warm and humid air from the house through the return air ducts. At the same time, a very cold refrigerant liquid enters the evaporator coil.

When the indoor air comes into contact with the coil, the refrigerant absorbs heat from the air, and that is how the air is cooled. The cooled air is then forced out through the supply air ducts.

The water vapor in the air (humidity) also comes into contact with the cold coil and condensation happens (the vapor turns into liquid water).

The water is supposed to drip into a pan and drained out of the house or even channeled into the main house plumbing. If your air conditioner is leaking, that is clearly not happening.

Why Your Air Conditioner is Leaking Water

air conditioner leaking through the roof
air conditioner leaking through the ceiling

Air conditioners leak for different reasons. Sometimes finding the source of the leak is easy while in other times you may need to bring an HVAC technician to locate where the problem is.

The following are some of the causes of a leaking air conditioner:

1. Rusted/Cracked AC drip

An air conditioner condensate drain pan also known as a drip pan is a tray located under the evaporator coil to catch the condensate as soon as it drips. The drip pan is connected to the drain line to drain the water outside the house.

You air conditioner may have one or 2 AC drip pans. If you have a vertical HVAC unit (where the evaporator coil is located above the furnace or air handler), you most likely have 1 drip pan.

On the other hand, horizontal HVAC units (usually installed in attics) have a primary and a secondary drip pan. The primary drip pan is installed under the evaporator coil while the secondary coil is big, visible and located under the entire unit.

Secondary drip pans are a backup for the primary units. If you therefore have a horizontal HVAC unit you will need to check both primary and secondary drip pans.

Evaporator Coil on top of AC Drip Pan

After years of usage, the AC drip pans which are made of metal are likely to corrode, weaken and develop holes. The alternating seasons where the pan has water and when it is dry and hot causes it to expand and contact further fastening its likelihood to crack.

Cracking affects both metallic and plastic drip pans. However, plastic drip pans are likely to last longer than metallic ones since they are corrosion resistant.

To see if your AC drip pan is the problem, check the level of water inside it (remember both primary and secondary drip pans). If the drip pan is full of water, then it is not leaking. The problem is elsewhere.

However, if the AC drip pan is not full of water and no water is dripping out of the condensate drain line, the drip pan is clearly damaged and leaking. Use a flashlight and check if you can see the holes/crack on the pan.

While fixing an AC drip pan is possible using a water-resistant sealant, I would recommend a replacement. That is especially if you have not replaced the pan in more than 10 years.

2. Clogged Condensate Drain Line

From the drip pan, the water is supposed to be removed outside through the condensate drain line also known as AC drain line. The drain line runs from the side of the drip pan to the outside of the house but in some instances it is connected to the bathroom sink drain.

Due to the humid nature inside the AC drain line, it is a perfect breeding ground for algae, mold, mildew and other such organisms. When you don’t clean the AC drain line regularly, these organisms will then rapidly multiply and block off the drain line.

Another cause for a clogged AC drain line is dirt particles. Even though your AC is fitted with an air filter, some particles will still pass through it and find their way inside the drain line.

Also, failure to regularly replace the air filter or having a poor quality or even wrong size of filter will have dust particles settling and clogging the AC drain line preventing it from draining water out of the drip pan.

When your AC drain line cannot drain the water out of the drip pan, the water level in the drip pan will increase causing the pan to overflow and hence a leaking air conditioner.

If upon inspection you notice that your AC drip is full of water and is even overflowing, you are dealing with a clogged AC drain line. Unclogging the drain will fix the problem.

How to Unclog an AC Drain Line

Luckily, unclogging an AC drain is so easy. You will only need a shop vac which you can even hire from your nearest hardware store for an hour. Unclogging the line takes less than 5 minutes.

  • Locate your AC drain line outside your house. It will be a PVC pipe ending a few inches from the ground, usually very close to your condenser unit.
  • Connect the shop vac’s hose to the AC drain line and use duct tape to create a tight seal.
  • Run the shop van for a minute or 2.
  • Dash inside the house and check if the drain pan has been emptied. If it has, you have successfully stopped your air conditioner from leaking.
  • Drain and clean the shop vac.

You can also use distilled white vinegar to unclog the line, although it takes longer. This is how:

  • Make sure the AC unit is turned off
  • Remove the cap on the drain lines access tee vent, which is inside the house near the air handler.
  • Check inside the line for any gunk that you can remove easily with your hand.
  • Pour 1 cup of distilled white vinegar down the drain line and wait for 30 minutes.
  • Flush the drain line with water (hot water if possible). Have someone stand outside next to the drain line to check if the water is flowing out. That should tell you that the line has been unblocked.

I have written a detailed guide on how to unclog an air conditioner drain line. Read it here.

3. Faulty or No AC Float Switch

An AC float switch is a small device that prevents your air conditioner from leaking in case of a clogged condensate drain line. If you have a horizontal AC unit it will be located in the secondary drip pan but if you have a vertical AC unit it will be located in the drain line.

The way the AC float switch works is such that when the water level in the drip pan is low (as it should), the float mechanism is at the bottom of the switch assembly. However, if the water level in the drip pan rises more than it should, the float mechanism moves up alongside the water level.

That causes it to break contact between 2 electric probes. When the contact is broken, electric current cannot flow to the AC unit and it therefore turns off.

Turning off the AC unit ensures that it can’t produce more condensate. As such, a float switch prevents your AC drip pan from overflowing, causing water damage.

AC float switch are however not foolproof and they also malfunction. When that happens, the AC drip pan will fill with water and overflow.

If your air conditioner drip pan has a float switch but still it is overflowing with water, you will need to unclog the drain line and replace the float switch.

Some folks don’t even have a float switch. If you are in that category, unclog the AC drain line and have a float switch installed.

4. Faulty Condensate Drain Pump

Some air conditioner indoor units are located in areas where the condensate cannot freely flow out of the drip pan via gravity. If your unit is in the basement or farther in the attic, it most likely uses a condensate pump to drain water out of the drip pan.

An AC condensate drain pump is a centrifugal pump which works like a sump pump. When the water level in the pan increases, the pump is activated and it pumps the water out through the drain line.

Just like all pumps, the AC condensate drain pump will fail at some point. When that happens, the pump will fail to empty the drip pan, and water will leak out of your indoor AC unit.

The solution for this problem is to simply have the pump replaced. Turn the AC off until the pump is replaced with a new one.

5. Improper Installation

Do you have a relatively new air conditioner that is leaking water from the inside? There is every change that it wasn’t properly installed.

You see, the AC drip pan is not very deep. If the installation is done in such a way that the unit or drip pan tilts to one side, water is likely to pool on that side and leak out even before the drain line has the chance to remove it.

This is especially bad if the unit tilts on the side away from where the AC drain line outlet is located. The good thing is that this is quite easy to detect.

Head over to where you AC indoor unit is located. Check if the unit looks tilted to one side. Better still check if there is water pooling on one side of the drip pan while the other side is dry.

If that is the case, you can have the technician come over again and fix the unit properly. You don’t even need to pay them again since they did a shoddy job and have even inconvenienced you.

Note: The AC drain line end outside the house also needs to be a few inches from the ground where nothing can block it. If the drain line happens to be lying on the ground and submerged in surface runoff, the atmospheric pressure will prevent the line from draining causing your drip pan to overflow.

6. Frozen Evaporator Coil

It is not unusual to have ice completely covering the evaporator coil. The freezing starts from the coil and can work its way back up to the air conditioner pipe outside the house.

So, why do air conditioners freeze?

Air conditioners freeze when the flow of warm air to the evaporator coil is restricted or when refrigerant level in the air conditioning system is low.

The causes of restricted airflow to the air conditioner evaporator coil are:

  • Blocked air ducts
  • Clogged air filters
  • Dirt evaporator coil
  • Leaking ducts

As a homeowner, it is not easy for you to inspect air ducts for leaks or clogs. That will need to be done by a professional technician.

However, you can easily replace the AC filters on your own. Ideally, AC filters should be changed after every 90 days or even sooner, especially if you have pets or there are many people living the house.

When the AC filter is dirty, the fan struggles to pull warm air from the house. That is also the case when the evaporator coil itself is dirty.

When the flow of warm air to the evaporator coil is restricted, the refrigerant inside the coil keeps on expanding. As I said, when the refrigerant expands, its pressure and temperature drops.

When the refrigerant temperature drops below freezing point, the moisture in the air will not drip on the pan but instead it will ice over the evaporator coil.

Low levels of the refrigerant also means that its pressure will drop and when that happens, its temperature will also drop below 32 degrees (freezing point) and ice will be formed all over the evaporator coil.

As I mentioned, freezing starts from the evaporator coil but will later spread back along the refrigerant line or even the supply air ducts.

After sometime when the AC turns off, the ice will start to thaw, and you will notice that your air conditioner will start leaking water. If your air conditioner is leaking and is not cooling properly, you most likely have a frozen AC.

I would advise that you bring an HVAC technician to inspect/maintain your AC unit and get to the roof of the problem.

Wrap Up

And basically those are the reasons why your air conditioner could be leaking water. I would also mention that scheduling regular maintenance by an HVAC technician will help you avoid most problems associated with air conditioners.