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The only thing I hate more than an air conditioner that doesn’t work is one that leaks water.
Air conditioners remove water from the air during the cooling process. The water produced from the air passing over the evaporator leaves the unit through a drain line.
Once that line clogs up, water can overfill the drain pan and destroy ceilings and walls.
Fortunately, keeping the water flowing is easier than you think. Just follow this simple guide to get your AC draining again.
Key takeaways
Common ways to fix an AC that’s not draining
There are a few reasons that an AC stops draining, but they primarily center around the pipe. Therefore, in the list below, I am focusing on water not coming out of the condensate line.
However, this may be hard to spot if an AC drains into a home's plumbing and will require professional assistance.
The AC hasn’t been turned on long enough
The first reason that an AC drain may not have water coming out is that it simply hasn’t been running long enough.
It takes several minutes for condensation to build up on the coils and run its course out of the house.
It is common to see very little water come out in the Spring and Fall when the AC unit is only running a few minutes at a time.
Solutions:
Don’t panic at the first sign of a dry drain line! Instead, keep an eye on the unit for a couple of hours or days to see if anything changes.
I would also take a minute to check the overflow pan (if equipped) to ensure water isn’t backing up into it. As long as water is not backing up in the unit or the overflow pan, then there is nothing to worry about.
The condensate drain line is clogged
A clogged condensate drain line is one of the main reasons for an AC not draining water.
Debris, such as insulation, can get caught up in the drain line, or more commonly, algae builds up along the walls of the small drain pipe.
A clogged drain line is almost always preventable with regular maintenance, but when left unchecked, it can cause significant damage to a home.
I have seen ceilings, walls, and even floors destroyed by a clogged drain line.
Because an air conditioner only produces a trickle of water, it is easy for a homeowner to overlook it.
Related article: Guide on how to clean your air conditioner
Solutions:
ACLAB Note:
It is also worthwhile to check whether you have properly installed the drain line in the first place.
Rusting evaporator coil and drain pan
Another reason water may not be coming out of the AC condensate line is that the air handler has rusted out.
It’s pretty rare to find a rusting air conditioning unit in an attic, but they are out there. Rusting is usually seen on older systems that are not properly serviced.
I came across one many years ago. The unit clearly hadn't been serviced in years, and the evaporator and air handler were rusting.
That let water flow into the overflow pan, but eventually, that rusted out, too.Galvanized overflow pans do a pretty good job, but they will start to rust if water sits in them for an extended period of time.
The one I worked on was only caught because the walls were wet. Unfortunately, that meant the house needed a ton of work in addition to the AC repairs.
Solutions:
In most cases, the only viable solution to rusted coils is going to be an air handler replacement.
If the outdoor unit hasn’t been replaced in recent years, then it is best to replace both at the same time.
If the drain pan has rusted through, but everything else is okay, then it is possible to replace it. I have replaced a pan for a short-term fix, but it is usually putting a bandage on a bigger problem.
Remember that rust from the drip pan can get into the drain line and cause clogs, creating an even bigger problem.
The drain line has accidentally disconnected
PVC pipe is by far the most common material used for an air conditioner drainage line. The one downside is that PVC pipe uses glue rather than a mechanical connection like threaded pipe.
Glued PVC pipe is very strong, especially when prepped properly and not under pressure.
However, in rare cases, water may freeze inside the pipe or get bumped, leading to joints failing.
When disconnected, water coming from the condensate pan may run into the house. The good news is that fixing a disconnected or broken PVC drain is easy for a homeowner to do.
Solutions:
Your AC is freezing up
When an air conditioner freezes up, condensation that normally drains outside freezes up on the evaporator coil.
Since the water is freezing up, it doesn’t drain out until the coils begin to thaw. Freezing occurs for several reasons, so there isn’t an easy answer to fix a frozen system.
In really bad instances, ice may actually block the drain pipe.
Solutions:
You have a broken condensate pump (applicable for central ACs)
When there isn't a downward slope from the air conditioner to the outside, HVAC contractors will often use a drain pump to help move condensate water.
Water from the condensate tray flows through a pipe and into the pump. It then pressurizes the water in order to move it vertically.
The pumps are very reliable, but they can lead to some major headaches when they fail.
Condensate pumps are not very common where I live. In fact, the first time I saw one was with a mini-split. They are becoming more common with newer construction because contractors are finding creative ways to hide drain lines.
Diagnosing a bad condensate pump is pretty straightforward. If water backs up in the pump and it has power, then it’s probably bad. It is possible that it is clogged, but if it’s not turning on, then it likely needs replacing.
Solutions:
The only solution to a broken condensate pump is replacement. Condensate pumps are readily available online, and replacing one is a DIY job. Simply disconnect the incoming condensate line and outgoing drain tube and reconnect it to the new pump.
I highly recommend placing a small collection tray underneath the pump if one isn’t already in place. A safety switch or alarm on the pan is also a good idea.
Incorrect P-Trap design (applicable for central ACs)
When I moved into my current house, water was flowing into the overflow pan and through its drain. I suspected a clogged AC drain, but after cleaning the line, I realized that wasn't the problem.
At some point before I moved in, someone had cut the AC drain line. They may have done this to clean the line or when they replaced the unit.
However, the added repair coupling raised the pipe just enough to put it on an upward slope.
Drain lines must be on a downward slope to remove water (unless the pipe is connected to a pump).
Another problem that leads to a unit not draining properly is forgetting a P-Trap. This simple curved pipe is required if the AC drain line connects to the home’s wastewater. However, some air conditioners also require them to keep water flowing.
When air flows through the indoor unit, it creates a vacuum on the drain line. A P-Trap prevents the system from pulling water back into the coil and allows for proper drainage.
Solutions:
The temperature of the air doesn't always create condensate
Circling back to my first point about the air conditioner not running long enough, it is also possible that the properties of the air in a house are not conducive to forming condensation.
To put it simply, an air conditioning system can remove water from the air. This water is categorized as condensation. If the air in the house is very dry (low humidity), then there will be very little condensation.
Most people are accustomed to seeing their cooling system drip condensate water.
However, just because you don't see water dripping doesn't mean there is a problem. As long as moisture doesn't collect inside the system, it is draining correctly.
Get your AC checked if these fixes don’t solve the problem
Repairing an AC unit that does not drain properly is often a project that DIY’ers can tackle. However, it is critical that the problem be fixed to avoid water leaking into the house.
When left unchecked, water backs up into the house, causing damage.
Even after the repair, the moisture can cause other problems like mold growth, leading to costly repairs.
If you are unable to clear a clogged AC drain line or find that the air conditioner drip pan is rusted, then it is important to get help. An HVAC professional will have extensive experience and can quickly remedy the problem.
They will also have tools like AC gauges, a wet-dry vacuum, and drain tools to efficiently remove standing water without causing further damage.
FAQs
Where is my AC drain line located?
AC drains are usually located on the outside of a house. Sometimes, the lines are located near the outdoor unit, but that isn't always the case. Sometimes they run into your home's plumbing.
Do all AC units have a drain line?
Nearly every air conditioning unit uses a drain line, including a conventional split system, a mini-split, and a package unit. Any type of split system with an indoor unit must have some sort of pipe or tube to remove moisture.
One exception is a portable air conditioner, which either uses a slinger ring that picks up water and flings it onto the hot condenser to evaporate the water, which then goes out the discharge hose.
Related article: Top rated self-evaporating portable ACs
How do I prevent water from backing up?
The best way to prevent excess water from backing up is to perform regular maintenance on the air conditioner.
What temperature should I set my air conditioner to reduce humidity?
There isn't a set temperature that reduces humidity in the air. Instead, you should set your temperature at whatever level is comfortable.
If the home still has a lot of moisture, consider a dehumidifier to remove more water from the air.
