Let’s clear this up: It is not normal for a split AC indoor unit to drip water indoors. If you see the water below the split AC indoor unit (stains on the wall, puddle on the floor, soaked carpet under the air handler), you do need to be alarmed. We are going to go through all 7 reasons why water might be dripping from the split AC indoor unit, what to check, and how to fix each of them.
Here’s why the confusion about the HVAC unit leaking water is so prevalent:
- Outdoor unit (split AC, heat pumps, mini splits) will leak from time to time. This is not concerning at all; at higher indoor humidity levels, it is quite normal to see water dripping from the split AC outdoor unit.
- Indoor unit should never leak. If you see water leaking on the floor beneath the split AC indoor unit, you do have a problem that needs fixing. Wondering “Why is my air conditioner leaking water inside the apartment or house?” is not just theoretical; you have to take the necessary action to find the why the wall AC unit leaking water inside. It’s like a busted water pipe; if you don’t fix it immediately, it will certainly cause further damage to your home.
Alright, let’s make an action plan to fix this. We are going to take a structured approach here. We are going to:
- Explain how the split AC indoor unit gathers and drains water outside; this is what it should be doing, but clearly it’s not doing this job well if you have water puddles or water stains below the indoor air handler.
- List 7 culprits that can cause water to drip from split AC indoor units on the floor, carpet, and so on.
- Go one-by-one and explain each potential reason why this is happening, illustrate how to check if this is the key culprit, and explain how to fix it.
Let’s start with how the split AC indoor unit should work:
How Split AC Indoor Unit Accumulates And Expels Water (Normal Operation)
Here’s the 101 on why there is any water in the split AC indoor unit:
AC cools the air by passing warmer indoor air over a very cold coil, located in the heart of the split AC indoor unit (for folks who know a bit of HVAC lingo, this is the evaporator coil). That is also where the indoor air humidity is reduced; the indoor humid air condensates on the cold evaporator coil (you can see water droplets on the coil).
When the indoor is working as it should, that water is channeled outdoors. Here’s how this goes step-by-step:
- Cold evaporator coil inside the split AC indoor unit captures excess humidity via condensation.
- Water drips into the drain pan, where it accumulates.
- The accumulated water is now channeled outdoors via the drain line (without or with the help of the condensation pump that actively pumps the accumulated water outside; some units have it, others don’t).
We can see the gathered water drip from the end of the drain pipe, located outside. Split AC is supposed to drip outside; not inside.
Understanding how the split AC indoor unit gathers and expels water is essential. If any of these steps go wrong, we have to deal with a split AC indoor unit leakage. Here is the list of what can go wrong:
Why Is Your Air Conditioner Leaking Water Inside? (7 Potential Reasons)
If you call an HVAC guy since you see water dripping from the air handler, he or she will go over this split AC indoor unit troubleshooting. Here are these most common reasons why the indoor air handler might be leaking:
- Clogged condensation drain line. This #1 reason why you would see water leaking inside the apartment or house from the indoor AC unit.
- Condensation line is disconnected.
- Hole in the drain pan.
- Faulty condensation pump.
- Dirty air filters.
- Low refrigeration levels.
- Split AC indoor unit is not installed correctly.
As we can see, the most common reasons have to do with the condensation line (reason #1, #2, and #4). This can be fixed with relative ease; for something like #6 low refrigeration levels, you will need help from an HVAC professional.
Let’s start with the most common culprit – condensate line blockage – and the more through the list like a professional would do:
1. Partially Or Fully (Blockage) Clogged Condensation Drain Line
After a while (or during the off-season), all kinds of dirt can fill the condensation drain line. We are talking accumulation of dust, dirt, debris, and so on. This sludge can block the condensation drain line entirely; it is also possible that you have mold growth, algae, or even fungi there.
If the condensation drain line is partially clogged, you will see water dripping from the air conditioner filter (from the front of the split AC indoor unit). If the condensate drain line is blocked entirely, you can expect the wall AC unit leak water inside (flow of water) since the line cannot channel the accumulated water from the drain pan to outdoors.
Here’s how to fix a clogged condensation drain line:
You have to remove the clog. First, you have to find the clog. Remove the front panel and the split AC indoor unit filters. Beneath the filters, you should find the drain pan and a small hole (about 1/2 inch in diameter).
If you see the cloggage, take a sharp object like a pencil, screwdriver, or smaller kitchen knife, and start poking at the cloggage. The goal is to disentangle that clog so the water can be drained effectively.
If you don’t see the cloggage, use a long wire and start poking it inside the drain line hole. Sink it deep and go back and forward to mess up the clog and relieve the drain line.
After you get rid of the cloggage, pour a good amount of vinegar into the hole. This will flush the clog out as well as kill the mold and algae that might still be inside the line. After you are done, the water drip from split AC indoor unit should stop.
If this doesn’t help, move down this list to find the main culprit:
2. Disconnected Condensation Drain Line
During the normal wear and tear the AC has to undergo, the condensation drain pipe might get disconnected from the hole in the drain pan. That would result in the water accumulated in the drain pan missing the drain pipe entirely, and the water will leak all over the wall beneath the split AC mini split indoor unit. You may notice prior stains on the wall.
Here’s how to fix a disconnected drain line:
You just have to connect it to the drain pan hole again. Again, open the front panel, remove the filters, and check if the water flows from the drain pan hole into the drain line. If not – you will clearly see if the line is disconnected – just take the line and slip it in over the hole (or in the hole; depends on the air handler model).
3. Hole In The Drain Pan (Cracked Pan)
The only job the split AC indoor unit drain pan has is to accumulate and hold water; this water is then channeled outdoors via the drain line. Again, due to wear and tear (mostly rust and the determination of the pan) or due to acute damage, there might be a hole in the drain pan. In most cases, we see a cracked drain pan leaking water droplets over the floor beneath the split AC indoor unit.
Here’s how to fix a damaged drain pan:
In all honesty, it’s best to replace the pan. Check the manual, find the model of the split AC indoor unit, and order a new drain pan. It should cost less than $30 for most models.
Alternatively, you can plug the holes with water-resistant tape or other types of sealant that is resistant to water. Once the drain pan is replaced or adequately sealed up, the indoor unit should stop leaking water immediately.
4. Condensation Pump Went Bust (If You Have It)
Bigger split AC indoor units (18,000 BTU, 24,000 BTU, or 36,000 BTU) accumulate more water. To facilitate the flow of that water outdoors, the unit might have a condensation pump that actively pumps the water out. Of course, many split AC indoor units do not have this condensation pump.
If that pump goes bust, the water is not effectively removed from the drain pan, and you will see the water reaching the drain pan edge. When it goes over that edge, you will notice the indoor unit dripping water on the left, right, in front, or in the back (where the drain pan edge is the lowest; it should be totally balanced, but it often leans to the left or the right).
Here’s how to fix a broken condensation pump:
You can’t. Even diagnosing if the condensation pump is not working as it should is quite a difficult job. In this case, it is best to call an HVAC professional to check if the faulty pump is causing the water to spill from the drain pipe inside your home. If that is the case, there is little chance the pump can be fixed; you replace it is almost 100% of cases.
5. Dirty Air Filters (Frozen Evaporator Coils)
Dirty air filters? Yes. Air filters with a lot of dust on them can lead to all sorts of AC problem, including water dripping from the split AC indoor unit.
This starts with insufficient airflow (due to dirty air filters) and may well end at the frozen indoor coils. Now, all that ice on the coils will, when left in warm indoor air, turn into water. The drain pan and condensate drain line usually cannot chug all that extra water, resulting in the drain pan overflowing.
Do we need to explain how to fix dirty filters?
Not really, right? You have to change them with new filters or wash them if your split AC indoor unit has washable filters. After the filters are clear, the airflow should again be sufficient, you won’t get ice on the evaporator coils and thus won’t have to deal with that extra water leaking on the floor below the air handler.
6. Low Refrigeration Levels (Again Freezing The Evaporator Coils)
Low freon levels can have the same effect as dirty filters, eventually leading to ice gathering on the evaporator coils. When the ice melts, the excess water will drip from the indoor unit on the carpet, furniture, floor, and so on.
Now, when you replace the dirty air filters, the leaking problem goes away. With low refrigeration levels, the problem is still there, and if you run the AC, the water will periodically leak from inside your apartment.
In this case, it is best to call an HVAC professional to rechange the refrigeration lines with R22, R134A, R410A, or whichever freon your AC uses. On top of that – and even more importantly – an HVAC guy will find the hole where the freon leakage started in the first place and seal it (before adding the right refrigerant).
7. Split AC Indoor Unit Is Not Installed Correctly
Brand new split AC mini split leaking water?
If you have a new split AC mini split unit and the indoor leaking starts when you turn it on, there has to be something with how the whole unit was installed. The range of inadequate installation problems is quite broad.
In this case, call the HVAC guy who installed the unit, and tell him or her about the indoor unit leaking inside. They will immediately know something is wrong (well, it’s their fault) and come to re-check the installation and fix the problem.
These 7 culprits cover well over 95% of all the split AC indoor unit leaking inside cases. If you go one-by-one, the chances of eventually hitting the right culprit are extremely high.