Why is my air conditioner leaking water? Expert advice to locate the problem

Common reasons why your air conditioner might be leaking water, with advice from the experts on what to do next.

Air Conditioner On Empty Wall With Modern Kitchen Interior Background
(Image credit: Getty Images)

If your air conditioner has started leaking water - it should be looked at as soon as possible. Signs of leakage may reveal problems or faults within the unit, and you'll want to avoid water damage to your home.

This is also why it's important to know how often you should service your HVAC system. These machines do a lot for us year-round, and with that comes the need for regular maintenance.

If cleaning your air conditioner hasn't sorted the issue, read on for common reasons why it might be leaking, with guidance from the AC experts.

Why is my air conditioner leaking water?

The reasons why your air conditioner might be leaking water range from common maintenance steps to deeper issues that'll almost-certainly require a technician's expertise. 

If you're familiar with AC repair, you could perhaps give the more fixable issues a go, but we recommend consulting the professionals to avoid any risk of damage or making the problem worse.

Air conditioner unit outdoors, next to large plant vase

(Image credit: Getty Images)

Clogged drainage

The condensate drain is the part of the AC system responsible for removing condensation from the evaporator coil. Because of its close proximity with moisture, it can easily cause leaks.

'A clogged condensate drain often happens in the spring and in the fall,' explains Rob Terry, HVAC contractor and owner of Terry's A/c & Heating. 'The drain can build up with slime, algae, and sludge when the air conditioner starts to run a little less often.'

A good way to test if this is the problem is by turning off your AC: 'When it comes to condensate drains that are clogged and leaking water down the walls or through the ceiling, the fastest thing to do is to turn your HVAC unit off. If that does not stop the water from leaking, the issue may be related to plumbing, not the air conditioner.'

If it isn't clogged drainage, the problem could be from poor-quality PVC pipes, or from clogged or worn-out drain pans, the (commonly) plastic trays designed to catch any leaks. 

Rob gives advice on what to do next: 'Homeowners should call a licensed air conditioning and heating professional who can diagnose and fix the issue. If it is a clogged drain, your HVAC technician can blow out the clog, show you where the pipe is and how to access it, and explain how to maintain it yourself.'

Blocked air filter

'Blocked filters are common culprits behind AC leaks. When the filter gets clogged, it restricts the airflow, leading to a buildup of pressure inside the unit, ultimately resulting in leaks,' reveals Lucy Arnold, Service & Maintenance Manager at PRA Air Conditioning.

Hopefully, this can be fixed by cleaning your HVAC system. 'The first thing you should do is clean the filters in the indoor unit,' Lucy advises, before checking the drain line is clear. If you have a can of compressed air, like the rechargeable MECO Cordless Compressed Air Duster from Walmart, you can blow this into the indoor unit to clear away any other blockages.

Many AC units have replaceable air filters, too, so in this case it might be time to buy a new one. If this doesn't work, however, Lucy recommends calling a technician to get to the bottom of the problem.

Melanie Powers, president of Goodberlet Home Services, adds that a damaged air filter can cause other problems within the AC unit: 'If the air filter is built up with dirt, air is unable to pass through evaporation coils, which leads to it freezing and ultimately leaking from the melting...'

MECO Cordless Compressed Air Duster | available from Walmart for $26.99

MECO Cordless Compressed Air Duster | available from Walmart for $26.99
A helpful tool to have for blockages in general, the MECO Cordless Compressed Air Duster can produce a strong 100000RPM airflow. It's rechargeable too, so you won't need to keep buying new cans. 

Frozen evaporator coils

Poor airflow from blocked air filters can often cause the evaporator coil to freeze over. 'If your system does not receive sufficient air, it can cause your evaporator coil to freeze up,' says Melanie, adding that this can then cause your entire system to freeze up.

'A frozen coil that is defrosting due to poor air circulation or low refrigerant levels can cause water leakage, but it is often not a huge flood of water all at once,' Rob clarifies. 

In the best cases, you can fix this by turning your thermostat all the way up to thaw the evaporator coil, Melanie suggests. However, if this doesn't work, it could be that the problem is more severe and your AC unit might be malfunctioning in some way. So, it's best to call a technician. 

Melanie emphasizes that a thermostat replacement is not always a DIY project; many homeowners do it wrong and fry their furnace control boards.' 

Refrigerant leak

'Refrigerant leaks can occur at anytime,' explains Traci Fournier, VP of Operations at One Hour Heating & Air Conditioning. The refrigerant helps to transfer heat and humidity outside of the home, so it's a vital component for the cooling process.

'A bubbling sound often suggests the possibility of a refrigerant leak,' Traci adds. If the problem is a refrigerant leak, or if you hear this sound, you'll need to call a technician as soon as possible. 'Refrigerant leaks will need to be professionally patched and recharged, which should be left to an expert.'

These are some common reasons why your air conditioner might be leaking water, but this isn't a complete list. If in any doubt at all, consult a professional who will understand the problem and how to fix it.

In the meantime, consider one of the best fans to keep you cool, and compare fans vs air conditioners to see whether all this maintenance is worth it.

Dan Fauzi
Home Tech Editor

Dan is the Home Tech Editor for Homes & Gardens, covering all things cleaning, smart home, sound and automation across the Solved section. Having worked for Future PLC since July 2023, Dan was previously the Features Editor for Top Ten Reviews and looked after the wide variety of home and outdoor content across the site, but their writing about homes, gardens, tech and products started back in 2021 on brands like BBC Science Focus, YourHomeStyle, Homes & Antiques and Gardens Illustrated.

Dan is based in Bristol, UK with a BA in Philosophy and an MA in Magazine Journalism. Outside of work, you'll find them at gigs and art galleries, cycling somewhere scenic, or cooking up something good in the kitchen.