Mini Split Air Handler Leaking Water On Floor? 5 Must-Check Causes

“Why is my air handler leaker water on the floor? Is it normal for water to be dripping from a split AC indoor unit?”

Not normal at all. If you see water leaking from the air handler and running down the wall on the floor, there is something wrong with the indoor AC unit. We are going to check all 5 culprits that cause the air handler to leak water from the bottom, and explain how to fix your dripping air handler.

First of all, it is important to note that the horizontal wall AC unit leaking water inside is not a good sign. If you see water droplets or even water stream down the wall from the mini split indoor unit, you should shut off the air conditioner immediately.

how to stop mini split leaking water on the floor
Trying to catch the water drops like in the photo is not the right way to deal with a leaking air handler.

Then you have to check for all of these common reasons why water is escaping the drip pan under the air handler (we will show you how one by one and how to fix a leaking air handler further on):

  1. Clogged air handler condensation line (fully or partially). This is the #1 cause of AC handler leaking water.
  2. Hole in the drain pan. If the drain pan under the air handler is damaged, the water might escape the indoor AC unit, and you will see a water stain under the air handler.
  3. Malfunctioning condensation pump. Some indoor mini splits have a pump that helps with the air handler drain pan drainage. If the pump is not working properly, the water will start leaking from the air handler down to the floor.
  4. Dirty air filters cause the indoor AC coils to freeze. If the airflow is restricted due to dirty filters allowing for less and less CFMs, the evaporator coils inside the air handler might freeze over. When that ice is melting, the condensation line, drain pan, or condensation pump might be overwhelmed, and the water will spill over the drain pan. We will notice this as the air handler leaking water on the floor.
  5. Low refrigerant levels. Similar to dirty air filters, low freon levels can cause the indoor AC coils to freeze over. When they melt, the amount of water released will be too much to handle, and the air handler will start leaking water from below.

If you see water stains on the wall under the air handler, your indoor AC unit is suffering from one (or several) of these culprits. The leakage basically happens because of two main reasons:

  1. Inadequate drainage (causes #1, #2, and #3 below). This will cause water to drip from the split AC indoor unit.
  2. Too much water due to AC evaporator coils unfreezing (causes #4 and #5 below).

To help everybody out, we are going to go over these culprits one by one, pointing out why the air handler is leaking water and how you can fix wall AC leaking water indoors yourself (DIY).

If you suspect that you have #3 and #5 problems, you will likely need to call your HVAC guy. At the end, we give some suggestions on HVAC guys in your area, if you will need one.

why is your horizontal air handler leaking water inside
Basic schematic of an indoor split AC unit that we will reference when fixing the leakage.

Let’s start with the most common reason for air handlers leaking water on the floor below the indoor AC unit:

#1 Clogged Or Partially Blocked Air Handler Condensation Line

When HVAC guys hear ‘mini split AC dripping water inside’, the first thing they think of is a clogged condensation line. That’s because, in more than 60% of cases, the reason why the indoor air handler is leaking water is a block in that line.

All mini-split AC units work as a dehumidifier as well (in addition to cooling). When the warm indoor air is passed over the cold evaporator coils inside the air handler, two things happen:

  1. Air is cooled.
  2. Moisture in the air is condensed on the coils, thereby reducing indoor relative humidity levels.

This water will drip from the evaporator coils to a drip pan, located at the bottom of a mini split air handler. From there, the accumulated water is drained outside via the condensation line (with or without the assistance of a condensate pump, more about that under #3 culprit).

Now, if you see a lot of water in the drip pan under the air handler, you probably have a clog inside the condensation line. Over time, dirt, dust, and even mold will block the condensation line. If this line can’t remove the condensate adequately, the water from the air handler drip pan will start to leak out of the fan onto the wall below the air handler and finally reach the floor.

Solution: If your split AC indoor unit is dripping water due to a clogged condensation line, you have to unclog that line. This might sound simple but it can be quite a hassle to unclog a condensation line.

Here are the step-by-step instructions on how you do that (Carrier has a useful article on how their HVAC technicians unclog lines here):

  1. Turn the air conditioner off.
  2. Locate the condensation drain pipe. It’s usually located at the bottom of the air handler (leading from the drain pan to outdoors with the pipe going through the wall). You will see a small hole in the drain pan (about 1/2 inches in diameter). This is the drain pipe opening.
    talking a leaking mini split indoor unit off the wall
    Be careful when opening the air handler. There are a lot of wires there that you don’t want to touch.
  3. If you find water standing in the drain pan, you will have to remove it. You can do that with a rag or use a wet vac to suck it all out.
  4. Clean the drain pipe opening, if there are any visible clogs there.
  5. Clean all the drain pipe by using a dry vacuum or wet vacuum. If there was a clog in your pipes, you will see that clog being sucked out by the vacuum. If you don’t have these vacuums, you can also use a garden hose to remove the blockage.
  6. Check if the clogging was removed. Just take a small amount of water and pour it down the drain pipe. If you see that water coming out in the outdoor pipe end, the clog has been successfully removed.
    troubleshoting air handler that was leaking water due to clogged drain
    If you see that the water reaches the end of the condensation pipe (located outdoor), you know there is no more clog inside the pipes.
  7. Optional: To make sure the clogging will not happen again, use a PVC piping cleaner and flush it down the pipe. If you don’t have PVC cleaner on hand, you can also use vinegar to clean the mini split AC drain pipe.

If there was a clog in the pipe (you sucked out black goo out of the pipe), it was causing the air handler to leak water inside. With the clog removed, you have successfully fixed the drip from the air handler. You can start the air conditioner again.

#2 Water Is Leaking Through A Hole In A Drain Pan

As we have mentioned under #1 cause, the drain pan accumulates the water before it can be safely piped outdoors. In some cases, we see a crack in this drain pan through which water drips from the air handler down the wall and on the floor.

There are several things that can create a hole in the drain pan, including physically piercing it with something, rusting, and so on. In most cases, older indoor AC air handlers can have a hole in the pan.

Solution: You have to fix that cracked drain pan in order to prevent water from leaking out of the air handler. Some basic measures include just tapping the hole where the water leaks out down with water-proof tape, using epoxy resin, or replacing the whole drain pan (useful and quite cheap if you have an older unit).

Once the cracked drain pan has been fixed, you should see that water has stopped leaking from the air handler.

#3 Condensate Pump Is Not Working As It Should

Some mini splits and heat pumps have a condensate pump. This pump expediates the drainage of the drain pan by pumping water outdoors (usually against gravity). You will usually see it installed in mini splits that are located on the lower floors or basements. On upper floors, the gravity will be enough to drain the accumulated water outdoors.

Needless to say, if the condensate pump in your split AC system is bust, the water will start to fill the drain pan until it spills over. We see this water spillage as water slowly dripping from split AC indoor units on low floors or in the basement.

Solution: First you need to check if the condensate pump is actually working or not. There is an insightful article about how to tell if the condensate pump is working properly by Blair’s Air here.

If you find out that the condensate pump is broken, you will likely need to replace it. Replacing a condensate pump in a mini split is not a simple DIY project; you will usually have to call your HVAC guy to check it out and replace it if needed.

When the condensation pump is working again, you shouldn’t see the water leaking from the indoor air handler anymore.

Now, all of these first 3 culprits were caused by inadequate drainage. The next 2 culprits we are going to cover are caused by excessive acute water production inside your air handler:

#3 Dirty Air Filters Causing A Frozen Air Handler Dripping Water Indoors

It is quite interesting to see how many air conditioner problems are caused by dirty air filters. If your air handler started leaking water on the floor, dirty AC filters might be the problem.

Here is how dirty filters can cause an acute rush of accumulation in mini split AC unit:

If the filters are dirty, the cold indoor evaporator coils (inside air handler) will get less airflow. Due to restricted airflow, the warm indoor air is not warming up the cooling coils quickly enough. This can lead to the indoor AC evaporator coil freezing over. You will start noticing that your AC unit started blowing warm air at first.

ac evaporator coil melting ice will cause indoor split ac unit to drip inside
This is what ice on the AC evaporator coils looks like. It’s of brownish color due to dirt accumulation. No usual transparent ice here.

All that warm air going over the frozen coils will start thawing the ice. Needless to say, that ice will get turned into quite a lot of water; more than the air handler drip pan can handle. As a result, you will start to notice the water running out of the indoor air handler and dripping to the floor.

Solution: First of all, you have to shut off the AC unit and wait for all the ice to melt. During this period, take a rag and soap the water that is being generated in order to avoid that water flowing down the wall under the horizontal air handler and damaging it.

Afterward, look at the air filters. If you notice a lot of dirt on them, it is quite possible that airflow restriction and the consequently frozen AC evaporator coils, and too much water inside the drain pan were all caused by dirty air filters.

Replace the air filters. Most HVAC experts recommend air filters be replaced every 1-3 months anyway. If indeed dirty air filters cause the air handler to spill water under your split AC indoor unit, the problem should go away with the new filters.

However, there is another culprit that can cause the air handler to leak water indoors in much the same way:

#5 Low Refrigerant Levels Causing Air Handler Leaking

Low refrigerant levels can cause similar AC evaporator freezing and the consequent melting of ice, ending in water coming from the air handler. In short, if the refrigerant is leaking, a chain of events can lead up to ice accumulation on the evaporator coils.

When that ice melts, it will overwhelm the drain pipe, and you will see that the access water is leaking down from the wall AC unit.

Solution: As before you would wait for all the ice to melt. During that melting use something to soap up the water and avoid carpet or wall damage.

It is very hard to recharge a mini split freon by yourself. You will need professional help. If you suspect that your mini split has low refrigerant levels (R22, R410A, and so on), you should turn off the AC unit and call your HVAC guy. He or she will measure the freon pressure, and help you out with recharging your AC unit.

All in all, if you see your air handler leaking water all over a carpet on the floor, or on the walls, you are facing two potential problems: inadequate drainage or access water.

Hopefully, you can use the understanding of the causes of the leaking air handler above to fix the leakage yourself.

If you need some help, you can use this form here and get quotes from up to 4 vetted HVAC guys in your area that will help you with a leaking mini split AC indoor unit.

In short, it is not all that hard to find out why your air handler is leaking water and fix it (either DIY or calling HVAC professional).

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