6 Reasons Why Your Window AC is Leaking Water

window ac

Your window AC is leaking water most likely because the drain tube or holes are plugged or the unit froze up and is thawing.

If you have a lot of water leaking inside and it’s damaging your house, shut your window air conditioner off and call a professional.

Learn the 6 reasons for leaking window ACs that I routinely come across working as a licensed HVAC contractor…

6 Reasons For Window AC Leaks

  1. Blocked Condensate Drain
  2. Clogged Up Air Filters
  3. Defective Condensate Drain Pan
  4. Defective Or Clogged Condensate Pump
  5. Refrigerant Leak Or Low Freon
  6. Poor Installation of Window AC

Reason #1: Blocked Condensate Drain

There’s a few different ways the condensate drain can plug up. Some units have holes in the back that allow the condensation to drain and can become plugged with dirt or other debris.

Other units have a condensate drain tube that can plug up more frequently because of its small diameter.

Mold, mildew, slime, and other debris commonly restrict these drains and allow the water to overflow.

Some newer models may have a safety feature that shuts the system down when too much water accumulates, but most don’t have this and can easily leak water if they’re plugged up.

I invite you to read my other guide on why the air conditioner (non-window) is dripping water here.

Reason #2: Clogged Up Air Filters

This is a very common problem with all AC units. Dirty or clogged filters prevent proper airflow and can cause your coil to get too cold and start icing up.

When the ice melts it has the potential to overflow or miss the pan and leak out of the unit.

Changing or cleaning your air filters is vital for proper operation and should be done on a regular basis. Read our tutorial on the signs your filter needs to be changed (and how often to change it).

Reason #3: Defective Condensate Drain Pan

If you’re dealing with an older unit, your condensate pan may be corroded or cracked.

The pan is what collects the condensate that forms when the AC is running, so if it has holes or cracks the water will leak through.

This can typically be seen fairly easily just by inspecting your window unit around the coils in the front and back.

Reason #4: Defective or Clogged Condensate Pump

Some systems can’t drain naturally and require a small pump to move the water to an appropriate place.

If your pump has a mechanical failure or obstruction, it can overflow and leak inside.

The pump will either need repaired or freed of the obstruction for proper water flow. You can read our guide on why the condensate pump is not working here.

proper slope for window ac unit

Reason #5: Refrigerant Leak Or Low Freon

A lack of refrigerant can cause your coil to freeze up just like dirty filters do.

The lack of pressure causes the coil to get too cold and ice starts to form and inevitably melts.

When it melts it usually overwhelms the drain and overflows or completely misses the pan and leaks into the house. I invite you to read our article on how to put Freon in window AC unit here.

Some refrigerant leaks can be repaired, but generally on a window air conditioner it can be a major repair and you may be looking at a replacement unit.

Reason #6: Poor Installation of Window AC

If your unit is new and leaking water inside, there’s a chance it wasn’t installed properly.

If the window unit isn’t pitched properly (sloping away from the house), it may not be able to drain correctly. You may need professional help to address this and correct the problem.

Frequently Asked Questions

Why Does An AC Make Water?

All air conditioners make water when they’re running. The cold refrigerant pumping through your indoor coil is lower than the dew point of the air in the room and allows moisture to condense on the coil. 

Picture a glass of ice water on a hot summer day. The outside of the glass is usually “sweating”. This is the same idea as what’s happening when your AC runs.

The condensation that forms collects at the bottom of the coil in the drain pan. From there it flows into a pipe or tube and drains away, usually to a floor drain.

Read Also >> Why Does My A/C Keep Freezing?

Why Is My Window AC Unit Leaking Water From The Front?

If small amounts of water are coming out of the front, it may just be small amounts of condensation that have formed due to a low set point and a very hot day.

This isn’t something to be overly concerned with and will dry up fairly quickly.

If large amounts of water are leaking inside, you probably have a clogged drain or frozen coil.

Make sure you regularly maintain your unit and this shouldn’t be a problem. If leaking continues you may need to call a professional to inspect and diagnose what is leaking.

How Do I Stop My Window Air Conditioner From Leaking?

Make sure you have clean air filters and check your drain lines.

You can even install condensate drain tablets to help reduce mold and mildew build up in your pan. They dissolve as condensation forms and help to keep things clean.

What Causes A Window AC To Leak Water?

Water usually overflows and leaks because of drain related issues or coils freezing up.

Sometimes though, a window air conditioner can leak water inside when it rains. Typically because it’s not installed or sealed properly.

Make sure you have your unit sealed around the window and leaning slightly toward the outside so that water naturally wants to flow toward the back of the unit.

RELATED: Why Does My AC Keep Running?

Final Thoughts

Window air conditioners make a good bit of water when they’re running.

Your window unit probably has water in it, even if it’s not leaking. This is normal and only a cause for concern if it begins leaking inside.

Making sure your filters and drain lines are clean can prevent your unit from flooding and creating expensive water damage. If you run into a problem where your unit is leaking, shut it down and determine where it’s coming from.

When in doubt, call a professional and get some help.


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