In the middle of summer many people notice the same thing: the AC is running, but there is moisture under the unit and wet marks show up on the wall or the ceiling. This is no less alarming than strange noises from the equipment. Owners often think right away of something serious, like a refrigerant leak or a problem with the compressor. In most cases, though, the reason is much simpler. The condensate line is clogged, and the water does not go out. It collects in the pan, overflows and runs down. When the air handler sits in the attic, that water has only one way to go, and that is into the ceiling.
Water in an air conditioner is normal. When the coil cools, its surface temperature drops below the so-called dew point, and condensate collects on it. That water then gathers in a special pan and is carried away through a drain line. This is a natural process. But if water comes out of other places and not from the drain line, that already signals a problem, and it needs to be dealt with. Ignoring these small things can hurt the equipment, and in a house it also hurts the ceiling, the walls and the furniture under them.
How an Attic Air Handler Drains
The indoor part of a central system, the air handler, has a coil, a fan and a pan under the coil. Condensate drips from the coil into the pan and leaves through the condensate line by gravity. For the water to run off properly, the line needs a certain slope. If the slope was set wrong during installation, leaks can form.
When it is hot outside, the system works longer and pulls more moisture out of the air. Several gallons of condensate can build up over a day. If the drain line is even a little clogged, the water starts looking for a way out, and that is when the leak appears.
If the drain runs by a complicated route, a small condensate pump is often added. It pumps the condensate and pushes it through the line to the drain point. If the pump fails, the water cannot reach the drain and starts leaking in all sorts of places. Condensate pumps are usually not repaired but replaced as a whole unit. This is a job for an HVAC technician.
ENERGY STAR lists the condensate drain of a central air conditioner among the things to inspect, because a plugged drain can cause water damage in the house and affect indoor humidity.
Why the AC Is Leaking Water Through the Ceiling
If the cause is found correctly, it is easier to choose a way to fix it that fits the situation. These are the main reasons an air handler leaking water in the attic ends up as a stain below.
Clogged Condensate Line
A clogged drain is most often the reason for a leak. Dirt and dust collect in the drain line, which then gets in the way of the water, and it comes out through other openings. Usually the clog forms from a mix of dust, dirt, small particles and slime that get into the pan from the filters and the coil. In a damp environment this mass quickly turns into a plug and blocks the water's path. Insects can also get into the outlet of the line looking for moisture.
With an AC condensate line clogged, the leak is noticeable right away. Sometimes water comes out in a thin stream. Sometimes only drops appear, and people do not pay attention to them at first.
Full or Damaged Drain Pan
The same problems can come up if the pan that collects condensate is dirty. If the pan is dirty, debris can block the drain openings, and the water will spill over the top. That can lead to serious trouble.
A damaged drain pan is found with careless installation of HVAC equipment. At first it may not be visible. So the leak happens slowly, but steadily. In this case the pan has to be replaced. The pan can also simply shift to one side, so the water drips past it. Another weak spot is where the pan outlet connects to the drain. If it is not tight, water seeps onto the housing parts and drips down.
Float Switch and Pump
A float switch reacts when water reaches a certain level. The float is linked to a switch and shuts the system off when it rises. The simplicity is its advantage. The drawback is that the float can stick because of dirt, and that leads to an overflow, because the debris keeps its moving parts from moving.
Other Causes
- Wrong slope of the drain line. The line has to be redone. This should be done by a qualified HVAC technician.
- Dirty filters. Clogged filters cut the airflow, the coil can ice up, and when the ice melts the pan overfills and a leak appears.
- Poor insulation on the refrigerant line. The tubes are much colder than the air around them. If the insulation is poor or done wrong, condensate collects on the line and drips from there.
- Refrigerant problems. A refrigerant leak can also be behind it. It usually comes with weaker cooling and ice on the unit. This is a serious fault, and it is better to call a technician.
AC Condensation Line Clogged Symptoms
Checking the drain is simple. If no water comes out of the drain line outside 10-15 minutes after the AC is turned on, the drain may be clogged. If the end of the line does not drip after long work in hot weather, a plug has most likely formed inside.
- No water at the outlet. In the summer heat the line should drip. If there is not a single drop, the line is most likely blocked.
- A steady stream instead of drops. With a normal drain, water drips from time to time. If a continuous stream runs, you need a proper check to find the reason and fix it soon.
- Water appears after every start. This, ice on the coil or worse cooling means a technician is needed.
- A stain on the ceiling or an AC vent leaking water from the ceiling. The water has already passed the pan and found its way down.
Keep in mind that no water at the outlet can have other reasons too. A clog, the wrong slope of the drain line, a kink or a break can all lead to no drainage.
What to Do Now
Turn the system off before anything else. A leak like this is quite dangerous, especially if the water can reach outlets, light fixtures or other electrical devices under the unit.
If you just wipe the ceiling and put out a bucket, the problem does not go away. Water keeps collecting, and the dirt inside holds moisture, causes a damp smell and blocks the drain again.
- Shut the AC off. If an AC leaks, it should not be turned on. With drain problems this is not critical for the equipment, but with a refrigerant leak running it this way can ruin the whole system.
- Protect what is below. Put a container under the drip and move furniture and things out of the way. If a lot of belongings are in the wet room, pack-out and contents protection services can move them out before more damage is done.
- Take photos. Photograph the ceiling, the wet spots and the place where the water comes through before you start cleaning up.
- Check the drain and do not start the AC until the water goes outside the right way.
Checking the Pan
To check the drain, with the power to the system off, you can pour 1-2 cups of water into the pan. If it drains, the line works. But it is important not to pour water on the control board or the wires. In the attic, step only on the joists or a walkway, never on the ceiling drywall.
If a simple check does not help, do not take the housing apart and do not use wire or household chemicals. This can damage parts or make the clog worse. When the drain is hidden in a wall, connected to the sewer, or there is a pump, it is better to call an HVAC technician.
While you look at the pan, check it for damage, for cracks in the plastic. Make sure it has not shifted to one side and that the connection at the drain outlet is tight and does not leak.
Ceiling Drywall and Insulation
When AC water drips, drywall, paint and furniture suffer. With an attic unit it is the ceiling drywall and the insulation above it that take the water first. The stain you see from the room is only the place where the water came through. The leak itself may have been going for some time.
Wet drywall and insulation take time to dry, and a quick look will not show how far the water went. For an assessment of a wet ceiling, read about our other water damage articles or go to the page on water damage restoration in Escondido.
Mold
In a constantly wet environment mold and bacteria multiply, which is especially dangerous for children, older people and people with weakened immunity. Constant dampness also draws mosquitoes and gnats, which fly into the drain opening. From there come more consequences.
If a stain or a musty smell stays after the leak is stopped, see the page on mold remediation for affected rooms. Our guide on preventing mold after a plumbing leak covers the first days after water gets into the house.
Preventing the Next Leak
Prevention is the best way to avoid leaks. Many owners have the system serviced once a year, in spring, before the season starts. Besides the check, the technician may also test the refrigerant charge. The ENERGY STAR maintenance checklist includes the condensate drain among the items to inspect.
If you noticed the leak in the heat, do not panic. Often the system simply cannot handle the volume of condensate because of a small clog. The main thing is to cut the power in time, check the drain and not run the AC until the water goes outside the right way.
You can learn more about our Escondido team, read what homeowners say in reviews, or go back to the water damage restoration home page.