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Why Is My HVAC Unit Leaking Water and What to Do

Why Is My HVAC Unit Leaking Water and What to Do?

mini split unit open various places

Source: monte_a/

When it’s sweltering outside and your HVAC unit is working overtime to keep you cool, it’s not unusual for it to produce water, but it should be contained within the unit itself and carried away in a drain pipe. If you notice water around your Mitsubishi mini split unit or leaking from the indoor handler, it’s important to get a professional opinion, no matter how minor the leak appears to be.

Why Is My HVAC Unit Leaking Water?

When you notice water around your HVAC unit, turn off the system to safely investigate. This can also prevent further water leakages and save your unit from electrical damage or mechanical failure. There are five main causes of water around your HVAC unit.

air filter before and after use

Source: RF-2020/

1. Clogged Air Filter

Air filters don’t process any water, but they can contribute to a leak if it’s dirty. A clogged air filter blocks the airflow that runs over the evaporator coils. When no warm air travels over the evaporator coils, it gets too cold and freezes. Then, when the AC unit turns off, the frozen crystals on the coils melt, and the sudden influx of water overflows the drain pan.

Changing the air filter should solve this problem. Depending on your unit and the amount you run it, you should change the air filter every month for panel filters and every 3-6 months for pleated filters to enjoy optimal AC quality and protect your HVAC unit from unnecessary wear and tear.

2. Leaky HVAC Drain Pan

If your HVAC unit is at least 12 years old, you may have a leaky HVAC drain pan. These pans start to crack and rust due to moisture damage and corrosion. 

A high-quality epoxy-based water sealant may solve the problem if the drain pan has a few minor cracks. However, more extensive damage will require a new drain pan, which must be welded into place by a professional.

3. Clogged Drain Line

After the clogged air filter, a clogged drain line is one of the most common causes of a leaky HVAC system. Because these lines continually have water in them, it is a breeding ground for dust, dirt, mold, and mildew, creating a blockage in the drain line. 

To clear a clogged drain line, you can suction out the clog with a wet-dry shop vac, but you are much better off calling a professional to service your HVAC system. They have special tools to clear the line, including a small plumbing snake, a high-powered wet vac, and a drain line cleaner.

You can pour 1-2 cups of bleach or distilled white vinegar into the drain line every few months to prevent clogs. This destroys mold and mildew buildup before it blocks the entire line, keeping your HVAC system running smoothly. 

4. Broken Condensate Pump

If your HVAC is in the basement and it’s leaking water, there’s a good chance a broken condensate pump may be to blame. These pumps are responsible for pushing water up to ground level and away from the house. 

When it stops working, gravity stops the water from moving up on its own, so it feeds back into the HVAC unit. When that happens, the water escapes out the bottom of the unit, leaving water on the ground. 

A broken condensate pump requires a professional to repair or replace it.

5. Low Refrigerant

Refrigerant is the chemical responsible for keeping the evaporator coil cool without freezing. In older models, the refrigerant is usually freon, but that has been replaced by the more environmentally friendly chemical Puron.

If you notice water around your unit and hear a hissing or bubbling sound coming from the refrigerant line, your water leak is probably due to low refrigerant levels. If this is the case, you’ll also notice that your unit is having trouble cooling the house; either it’s too warm, or the unit runs excessively.

If low refrigerant is the cause of your water leak, you must keep the unit shut off until you can have it serviced by a professional. A lack of refrigerant has the potential to destroy your entire HVAC system.

AC technician with tools and parts

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What Do I Do?

Water around an HVAC unit can cause water damage, grow toxic mold, lower overall air quality, and even cause complete HVAC system shutdown if not addressed.

HVAC units should be serviced once a year so you can be proactive about catching any potential water issues before they happen. 

If your HVAC unit needs replacing, consider upgrading to a ductless system. Our energy-efficient mini split AC costs less than a traditional HVAC unit, and many options come with smart technology to help you save even more on your monthly bills. Explore our range of mini splits from trusted brands, including Gree, Mitsubishi, and LG.

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