Why is My AC Leaking Water?

I lived in Houston, Texas for about 12 years in the 1990s and early aughts. Houston remains one of my favorite cities for its diversity, arts and music scenes (I worked at the Alley Theatre) and staunch resistance to any kind of residential or business zoning laws. The former two may surprise someone who has never been there, but Houston is much more than rich oil executives and cowboy boots.

It’s also built on a swamp and has the kind of hot, humid weather that requires year-round air conditioning and an army of ceiling fans. While there, I lived in a few different places and owned three houses (not at the same time), each with either window AC units or central HVAC systems (of varying ages and efficiencies). As any homeowner on a budget knows, you learn a lot about home repair and maintenance through trial, error and lots of cursing. 

AC units can develop a range of problems and issues when not maintained and serviced regularly, some of which can cause water leakage. There are also some issues that can develop despite regular maintenance which can also result in leaking water.

“Refrigerant leaks, for instance, can occur at any time,” says Traci Fournier, VP of Operations at One Hour Heating and Air Conditioning. Refrigerant helps transfer heat and humidity out of your home, cooling the space. 

“If your system has a refrigerant leak, it will need to be professionally patched and recharged,” said Fournier.

This isn’t the only issue that can cause your AC to leak, though. As well as Fournier, I also talked to Glenn Wiseman, certified technician and sales manager at Top Hat Home Comfort Services, a home improvement, maintenance and repair services company in Ontario, Canada and Michael Rubino, a mold and air quality expert, environmental wellness advocate, and founder of HomeCleanse, a mold remediation company that also studies indoor air quality, about air conditioners and what might be causing yours to leak. 

Common reasons for AC water leakage

Ideally, have your system serviced at least once a year during which an AC tech will check for leaks as well as examine the entire shebang to catch any other problems that might exist. If you live somewhere with weather like Houston, you may want to service your unit twice a year.  Here are some common reasons your AC may leak water. 

Clogged condensate drain

The condensate drain line runs through your home from the portion of your central AC unit that is inside the house (the air handler) to the outdoors. Made from either PVC or metal pipe, they provide a path (or funnel) for humidity and condensation created by the evaporator cables to exit to the outdoors. 

While it's normal for water to drip from the part of the pipe that extends out of your house, if something blocks the end of the pipe or debris or gunk builds up somewhere inside it, the condensation has no escape route which will cause leaking inside your home.

If you consider yourself pretty handy, you can try to clean it out yourself, but, often it's best to call a professional. If you want to try to clean it yourself, keep reading (I provide some instructions further on). 

Damaged drain pan

All central AC units have a condensate drain pan that collects water created by (you guessed it) condensation. Part of the evaporator coil unit, they are situated underneath it to collect water with the drain pipe extending from it. 

Units installed in attics (like all of the ones I had) also have a secondary pan fitted under the entire appliance. These days, the pans are most often made from plastic (to avoid rust issues that can happen in metal pans). Located directly above or below your HVAC system, condensate pans receive a blast of hot air during every heat cycle which can eventually cause cracking.

“Call a professional to resolve this issue and seal it properly,” says Rubino. 

Disconnected drain line

Your drain line could also be disconnected which can be caused by improper installation or an especially energetic and destructive squirrel who has found their way into your attic. To prevent animals from entering your attic, trim any nearby tree branches; I say this from personal experience. 

Frozen evaporator coils

You’ll probably notice frozen evaporator coils before your AC begins leaking as this scenario will likely mean that your unit has ceased to blow cold air. 

The prime culprit for frozen coils is reduced air flow, most often caused by dirt and debris build up on the coils. If you run your system with a dirty air filter, dust will settle on the coils (or mold can grow). Both of these things inhibit the coils from getting enough air flow which means they become too cold and freeze.

 “When this ice melts, it can overflow the drain pan and cause leakage,” says Rubino. 

Low refrigerant levels

A low refrigerant level can also cause your unit to get too cold which will, in turn, result in frozen coils. As the evaporator coils thaw and refreeze, they will drip excess water into the drain pan. Over time, this can result in your drain pan becoming too full. 

Damaged insulation

AC coils have insulation that keeps condensation from accumulating on them. If this insulation develops cracks or holes, the coils may leak water from the condensation.

“This will require a professional to assess and fix the issue,” says Rubino.

DIY troubleshooting tips

While leaks usually occur near the outdoor condenser unit, you may first notice that the AC is not running at peak efficiency or making a hissing noise.

“Loud hissing often means air is escaping where it shouldn’t,” says Fournier. If the sound comes from inside your walls, it could indicate leaky ductwork. If it comes from your vents themselves, your vent flaps damper might be too tightly closed.

“You might even hear this sound coming from the area of your filter if it doesn’t form an adequate seal,” she said.

“If you detect a bubbling sound, this often suggests the possibility of a refrigerant leak,” Fournier continued. Call an HVAC technician right away if you hear this one, she warned, as it can cause extensive problems

Even if you don’t hear either of these noises, if your unit leaks water the first step is to turn it off, says Wiseman.

 Then:

1. Check your air filter and change it if it is dirty.
2. Inspect the evaporator coils. If they are frozen, allow them to dethaw while you change the filter.
3. Clean the coils themselves with a damp cloth or brush, removing any dirt or debris.
4. Turn the machine back on; if it refreezes, call a professional, says Rubino.

If your coils are not frozen but the leak persists, check the drain pan for cracks and the drain pipe for any blockages. Further instructions for DIY cleaning of your drain pipe can be found below.

“Leaks can be due to issues with the coils, the suction line drier or the accumulator, so it is best to have a professional take a look who can tell you exactly what you’re dealing with,” says Wiseman. Accumulators, if you’re wondering, stop and store refrigerant so that it doesn’t get into the compressor while suction line driers remove moisture and acid while filtering out contaminants. 

When to call a professional 

 “If your system has a refrigerant leak, it will need to be professionally patched and recharged, which should be left to an expert,” says Fournier.

Wiseman advises that, as soon as you notice a leak, identify (if you’re able) where it is coming from, wipe away any moisture; then call a professional.

“You may try checking the compressor fan, evaporator coils and drain pipe and line, but if you are not sure what is wrong, wait for a technician to assess,”  he said, “In very rare cases, a homeowner without experience should try to fix the issue.”

In my experience it’s sometimes possible to remedy a blockage in your drain pipe on your own if it's relatively accessible and you’re comfortable crawling around in your attic. Anything beyond that is usually best left up to a professional. 

Preventive maintenance tips 

“Water dripping from air vents (or other places) pose various problems, potentially causing damage to your home and disrupting the efficiency of your HVAC system,” says Fournier.

You can help mitigate many potential problems by routinely inspecting your system for blocked or clogged ducts. Also, ensure that the condensate drainage line is unobstructed and clear of debris for proper drainage.

“Additionally,” suggested Fournier, “consider insulation to prevent condensation.”

Adequate insulation (of your home) helps regulate temperature and reduces the likelihood of water droplets forming on your vents. Adjusting humidity levels in your house decreases excess moisture in the air, thereby reducing the chances of condensation, she explained.

Equally important are regular maintenance tasks such as cleaning and replacing air filters and scheduling appropriate HVAC inspections. These can help uncover leaks before they become problematic.

“Promptly fixing any leaks or issues safeguards against water damage and helps enhance the efficiency of your HVAC system, creating a comfortable, dry indoor environment,” says Fournier.

Rubino recommends having an HVAC service technician assess the unit twice a year; once in the spring and once in the fall, before the system switches settings.

Make sure the technician tests for mold so that if there’s a problem, it can be resolved before turning on the unit and blowing it throughout the home.

“The technician should also clean the coil, make sure the blower, furnace, and cabinets are clean, and ensure that everything is operating correctly,” he said.

Frequently asked questions (FAQs)

Can I run my AC if it is leaking water?

“If you aren't sure what is causing your leak,” says Fournier, “it may be best to shut off your unit until you resolve the problem.”

This will help avoid the system overworking which can lead to a compressor failure.

How do I unclog my AC drain line?

“Clearing a drain line requires certain equipment, notably a wet/dry shop vac and possibly an air compressor,” said Fournier. If your air handler is located in your attic, it will also require working up there, possibly in a tight space. If you’re unable to do this or lack the equipment, she suggests leaving this job up to an HVAC technician. It’s a quick emergency repair that they’re accustomed to doing often.

Wiseman says that if you have a vacuum with a tube attachment, such as a shop vac, you can suck out water from the drain line.

“If there is a further obstruction, you may have to turn off your unit and check the drain trap, which requires cutting the tube,” he said, which he does not recommend doing on your own.

How do I stop my AC vent from leaking water?

 “You likely need to unclog the drain line, as suggested above,” said Wiseman.

Is AC leaking an emergency?

“With leaks, it doesn’t take much for a small problem to evolve into a bigger one, so it makes sense to call in the HVAC pros when you suspect you have this issue,” said Fournier.

Whether or not it's an actual emergency depends on the cause, said Wiseman.

“For example, refrigerant leaks can be potentially dangerous to your health if not remedied. In general, because you should not run the unit while it is leaking, it is best to have a technician come check it out ASAP.”

Related: The Best Air Conditioners Brands to Reliably Keep Your Home Cool