6 Reasons Why Your Air Conditioner Is Leaking Water

ac leaking

One of the most common service calls I receive in the summer months is for an air conditioner that’s leaking water.

While there are several reasons for water to be dripping from your air conditioner, the most common cause is a clogged condensate drain line.

When warm humid air is moved through a cold coil, condensation forms and collects in a pan. This condensate has to be drained away, typically through a PVC pipe or vinyl tubing.

This pipe or tubing is the condensate drain line and frequently gets clogged causing the collected water to overflow.

6 Reasons The AC is Leaking

  1. Clogged Condensate Drain Line
  2. Dirty Air Filter
  3. Low Refrigerant Level
  4. Faulty Condensate Pump
  5. Damaged Drain Pan
  6. Improper Installation

Reason #1: Clogged Condensate Drain Line

The environment and application of a condensate drain line create a perfect place for clogs to form.

Dust, dirt, slime, and other debris will form inside the pipe and prevent the water from flowing properly. From there, it overflows and runs all over the furnace or the floor creating a significant mess.

You can usually tell if the lines are clogged just by inspecting it. If there’s water everywhere but nothing coming out of the line, there’s a really good chance it’s clogged.

Removing the line and clearing it will fix this problem. Some can be removed and put back together fairly easily, and others may have to be cut and reconnected. Once the line is removed, you should be able to blow through it and clear it that way.

If I can’t blow through the line, I usually use a shop vac at the outlet of the drain line or compressed air to clear it. Using compressed air or CO2 creates a lot of pressure and can cause quite the mess. Try blowing through it and using a shop vac first, and if that doesn’t work move on to something with higher pressure. 

Be advised, a substantial amount of water will flow once the line is removed and the clog is cleared. It’s best to be prepared with a bucket and towels or rags to help prevent any additional mess.

RELATED: Why Water Is Coming Out of Furnace?

clogged condensate drain

Reason #2: Dirty Air Filter

A dirty air filter is a common a cause for why your air conditioner is leaking water.

Proper airflow allows your AC unit to transfer heat properly. If the filter is restricting airflow, your evaporator coil will get too cold and the condensation that’s forming on the coil will freeze. It creates a big block of ice on top of your furnace.

As the ice melts, it leaks water everywhere. It’s usually too much for the drain pan to handle causing it to overflow, and some of the ice will block parts of the pan preventing water from flowing properly.

Turn your AC unit off and allow it to thaw to correct this issue. Place some towels and rags around your furnace and coil to help catch some of the overflow and leave the fan in the on position to help thaw it quickly. 

Remove the old air filter and wait until it’s thawed completely. Once thawed, install a new filter making sure it’s oriented correctly. Airflow should point toward the furnace.

If you’re dealing with a frozen coil, check out our guide on how to defrost AC units!

Reason #3: Low Refrigerant Level

An air conditioner that has low refrigerant levels will have similar issues as a dirty air filter.

The low pressure causes low refrigerant temperature and will cause parts of the evaporator coil to freeze. Just like the dirty filter, as the ice on the coil melts it leaks everywhere and will have to be thawed before the problem can be corrected.

If you haven’t had any work done on your AC there’s only one reason for low refrigerant levels. Your AC is leaking refrigerant. Whether you have a fitting that leaks or a pinhole leak in one of the coils, it will have to be repaired to prevent further issues from arising.

Depending on the age of the equipment and the size of the leak, you may be further ahead to look at replacing the unit rather than repairing it because of the cost of fixing certain leaks.

If you think your AC unit has a leak, I recommend calling a professional to diagnose it properly. Refrigerant is dangerous and should only be handled by qualified personnel.

If you are interested in how to add refrigerant to your air conditioner, I invite you to our article on how to replace freon in AC units!

Reason #4: Faulty Condensate Pump

A faulty condensate pump is another typical culprit for an air conditioning unit dripping water.

A condensate pump is a small reservoir that collects the condensate from the AC with a pump to carry the water away. These are generally used when there’s no floor drain close by or when no drain is available at all.

The pump uses small 3/8″ vinyl tubing as a discharge line that can kink or plug up over time. If this happens, the reservoir will overflow. If the condensate pump has a safety switch, it should shut your AC unit off preventing it from continuously adding more water to the reservoir. 

The reservoir consistently holds water and is a breeding ground for bacterial growth. Slime is a type of bacterial growth that commonly forms inside condensate pumps and can cause the lines and pump to clog.

Using a diluted bleach and water mixture in your condensate pump should eliminate slime buildup and help prevent it from coming back. If damage is done and the pump is faulty, it can very easily be replaced and they are typically inexpensive. 

For additional information on verifying your condensate pump, check out our guide on how to test a condensate pump!

Reason #5: Damaged Drain Pan

Over time the drain pan under the coil can wear out and leak water through the bottom.

The drain pan is usually a molded plastic part that sits under the evaporator coil to collect the condensate that forms when running the AC. The condensate line connects to this pan to drain the water away.

Older air conditioners used metal drain pans under the evaporator coil that would rust out. Newer air conditioners use plastic pans, so rust and corrosion aren’t a concern. These plastic pans can crack and melt though which will definitely cause water to leak from your AC.

In my experience, excess heat will damage the pan causing it to crack or, in serious situations, melt. Usually a furnace related problem over the winter that creates a high heat scenario can damage the pan and will go unnoticed until you use the AC unit and find it to be leaking.

Damaged pans usually can’t be repaired and will have to be replaced. This type of repair is best done by a professional.

Read Also >> Can Window AC Units Be Recharged?

drain line sloping in wrong direction

Reason #6: Improper Installation

Air conditioners have to be installed properly to prevent water from leaking.

Although condensate drain lines are easy to install, they can be installed incorrectly. If being installed in an application where the coil is below or behind the blower, a condensate trap is required to allow proper flow.

The trap fills with water and stops air from the blower from being drawn into the condensate line. Without the trap, the negative pressure from the blower prevents the water from draining naturally with gravity.

Unglued or overtightened fittings will also leak. Over tightening a PVC fitting into the outlet of the drain pan can cause the pan to split. If this happens, the pan will need to be replaced.

If the condensate line is pitched in the wrong direction, it will cause the pan to overflow. There should always be fall away from the outlet of the coil. Condensate drain lines use gravity to move water, which means the coil outlet has to be the highest point of the drain line.

Read Also >> Why My AC Won’t Turn Off?

Prevention Tips For AC Units Leaking

Regularly maintaining your air conditioner is the first step in preventing water from leaking.

Condensate drain lines and traps should be cleared every year. Diluted bleach or vinegar is a great cleaner to help mitigate clogs and stop leaks from forming.

Checking and cleaning air filters frequently is essential for optimal performance and to prevent your coil from freezing up. 

Having your refrigerant levels checked annually can help identify potential issues and keep an eye on the performance of your equipment.

Professional maintenance is recommended to ensure everything is up to par and to prevent breakdowns and leaks from occurring. 

Frequently Asked Questions

How Can I Stop Water Dripping?

You can stop your AC unit from water dripping by removing and clearing the condensate drain line. Also try replacing your air filter in case your evaporator coil had iced up.

Should I Shut Down The A/C Unit During A Leak?

Yes, it’s best to shut your AC unit down until you can address what’s causing the leak. If left on, it will continue to leak while you are trying to repair it.

What Is The Best Way To Clear A Condensate Clog?

You can clean a clogged condensate drain line by disconnecting it and blowing through it or using a shop vac at the outlet to remove any debris.

Can I Use Hot Water?

Hot water by itself most likely won’t unclog the line. Its best to try a diluted bleach or vinegar mixture to help break down the debris causing the clog.

How Often Should I Clean The Condensate Line?

Your AC drain line should be cleared annually. It should be cleaned during regular AC maintenance.

Is It Normal For Water To Drip From Drain Line?

It’s only normal if the pipe is dripping in the right location. Water dripping or running at the end of the line is normal. If it’s at the beginning where the coil is located, this is a sign that you have an issue that needs addressed. 

Final Thoughts

If you find yourself with an air conditioner that leaks water, it’s probably something simple.

Start by changing your air filter and checking your condensate drain line. Have some towels and rags readily available to clean up the excess water.

The quicker you address the problem, the better off you’ll be. Water damage can escalate quickly and you also risk mold growth if left unattended.

Air conditioner leaks are really common and can be easily addressed by a professional if you feel in over your head, so don’t hesitate to call if need be.


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