Why Do Some Portable ACs Have Two Drains?

If you take a look at the back of your portable AC, you might see two drain ports: one on the top and one on the bottom.

But why are there two drain ports, anyway? Do you need to empty both of them? And which one do you connect the drain hose to?

The upper drain is used to connect a drain hose for continuous draining, while the lower drain is used to empty the condensate collection pan or tank.

In this article, I’ll go over the difference between the two drain ports that are on some portable ACs. You’ll learn why only some portable ACs have two ports, and why you don’t really need to hook up a drain hose to either of them!

Self-Evaporating Portable ACs Have Two Drains

The upper drain on a portable AC is meant to be connected to a drain hose for a continuous drain setup.

A continuous drain hose is only needed in very humid areas, or if you’re running your portable AC in dehumidification mode.

The lower drain port on a portable AC is used to drain all the water out of the AC when moving it around or storing it after you’re done using it.

You shouldn’t need to empty the water out of the lower port unless you’re moving your portable AC, storing it, or if it fills up with water and stops running.

The upper and lower drain ports on a portable AC are connected to two separate drain pans – the upper drain pan and the lower drain pan.

  • The upper drain pan collects condensation from the evaporator coil.
  • From the upper drain pan, the condensation flows into the lower drain pan where it pools.

So why does the condensation just flow down to the lower drain pan and pool up?

Self-evaporating portable ACs have a device called a condensate slinger.

The condensate slinger or “splasher” splashes water from the lower condensate pan onto the condenser coil. That’s why some portable ACs sound like a waterfall when they run!

The splashing of water serves two purposes:

  1. The splashing helps cool down the condenser coil and increase the efficiency of the portable AC.
  2. The splashing of condensate on the warm condenser coil will evaporate the condensate and blow the vapor outside through the exhaust hose.

So that’s why self-evaporating portable ACs always have a little bit of water in them – the splashing is what makes portable ACs self-evaporating!

But that brings us back to the upper drain port – why is it even necessary? Doesn’t all the water from the upper drain pan just flow to the lower drain pan anyway?

The upper drain port serves as a condensate drain in case too much condensation is produced by the evaporator. This usually only happens in humid climates, or if you run your portable AC in dehumidification mode.

That’s why you connect the drain hose to the upper drain port, not the lower one. The portable AC can do its job to remove most of its condensation by evaporating it from the lower drain pan and blowing it outside with the exhaust air.

The upper drain port just serves as a “backup” drain to be used used in humid climates.

Self-evaporating portable ACs need some condensation in the lower drain pan. If you connect your drain hose to the lower drain port, then the self-evaporating feature of your portable AC won’t work!

Which Drain Port Do You Empty the Portable AC From?

If your portable AC has two drain ports, you only need to empty the bottom drain port when moving or storing the AC.

It won’t hurt to empty your portable AC from the upper drain port as well – but you’ll find that not much water will come out since most of it drains down to the bottom pan.

However, if you live in a humid area or find it necessary to set up a continuous drain hose on your portable AC, then you should empty the upper drain port since your portable AC will collect lots of moisture.

Do You Need Two Drain Hoses for Portable ACs With Two Drain Ports?

You do not need two drain hoses for portable ACs with two drain ports. You only need one drain hose attached to the upper port.

Most times, you won’t need any drain hose at all – unless you live in a humid area.

Portable ACs with two drain ports are self-evaporating – so they automatically drain themselves by evaporating the condensate and blowing the vapor outside through the exhaust hose.

What Happens if You Don’t Use a Drain Hose on Your Portable AC?

If you have a self-evaporating portable AC, then you don’t need to use a drain hose unless you live in a humid area.

If your portable AC is not self-evaporating, then you will eventually need to empty its condensate tank from the drain port on the back of the portable AC.

So how do you know if you have a self-evaporating AC?

The easiest way to tell if your portable AC is self-evaporating is to check if it has two drain ports. The upper drain port is used to connect a drain hose, while the lower drain port is used to empty its lower drain pan while moving or storing the portable AC.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

15 thoughts on “Why Do Some Portable ACs Have Two Drains?”

  1. Interesting post. My portable AC (Comfort-Aire PSH-141D) has 3 drains. I understand that the upper drain port has to be used for continuous draining when the AC is on dehumidifier mode. The middle drain port has to be used when the AC is on the heating mode. And the lower drain port has to be used when the AC is on cooling mode and when a sensor indicates that the condensate pan is full. In this latter case, there is no continuous draining possible, probably because this AC is self-evaporating. I would appreciate if you could confirm my understanding because the owner manual is not very clear. Thanks.

    Reply
    • Hi Yves,

      You can use the upper drain port to continuously drain your portable AC when using it in cooling mode.

      However, I would not recommend that you continuously drain your self-evaporating portable AC unless you find that its condensate pan is regularly getting full due to a high humidity environment.

      The condensate in a self-evaporating portable AC splashes over the condenser coil and evaporates away to increase the efficiency of the portable AC. If you continuously drain your self-evaporating portable AC, then it will see an efficiency loss due to the lack of condensate cooling off the condenser coil.

      Hope this helps,
      -Trey

      Reply
  2. Thanks for your article. The bottom plug on my Midea portable AC is very close to the floor. What does one use to collect the water? I don’t see how any pan will fit under that (maybe a baking sheet?) Other articles have said to move the AC to a sink or bathtub, but this weighs approx. 80 pounds. Many thanks.

    Reply
    • Hi Brian,

      Yeah, moving the portable AC to a surface where you can empty it is always a challenge. If you have some steps you can move the portable AC to the edge of the steps and put the container on the step underneath. Otherwise, the only other thing you can do is lift the portable AC onto an elevated surface and put a container underneath it to empty it. If you need to lift a large unit, I recommend getting someone to help you.

      -Trey

      Reply
  3. Thanks for the post. I have an LG LP1217GSR – very similar to the one pictured. What I do not understand is the relationship between the self-evaporating feature and the dehumidification/dry mode. If I am using Dry mode, with the exhaust hose disconnected and a drain pipe attached to the upper drain port (as suggested by the sticker on the back), then wouldn’t I *not* want the self-evaporating feature blowing the moisture back into the air? And yet, from what I can tell, there is no functional difference between Dry mode and Cool mode. Unless Dry mode disables the condensate slinger, which I cannot see without disassembling the unit (Can you confirm whether this is the case?). Or unless connecting a hose to the upper drain port prevents water from draining into the lower drain pan (does it?).

    The unit has been running for several hours on Dry mode at over 50% relative humidity, and very little water has drained through the upper drain port. I’m confused about where all that moisture is going. If I turn the unit off, water flows from the drain port (presumably because the fan is no longer suspending the droplets on the evaporator coil). But otherwise, it doesn’t seem to be doing anything at all.

    Reply
    • Hi John,

      Great questions – you’re correct in your assumptions.

      When the portable AC is in dry mode the condensate slinger is disabled. And connecting a hose to the upper drain port (mostly) prevents water from draining down to the lower drain port.

      On your AC unit it seems like the pressure differential created by the evaporator fan motor keeps some of the accumulated moisture inside the pan. But the water will drain out freely once the negative pressure from the fan is gone.

      It seems like everything is working ok – how humid was your room to begin with? I’m also curious how much moisture has accumulated in your unit – maybe the unit holds a certain volume of moisture before expelling it from the drain hose?

      Hope this helps,
      -Trey

      Reply
      • Hi Trey,

        Thanks for your response. I made an additional observation. I think you are correct about the negative pressure holding back the water from draining out. I rocked the unit back and forth and a trickle began to flow down the pipe. Once this happened, the humidity in the room began dropping within 10 minutes. The temperature of the exhaust also increased by several degrees. Which suggests that even in Dry mode, condensate which doesn’t exit through the upper drain port still drips onto the condenser and gets evaporated into the exhaust.

        I believe that the reason for this is that once the flow started through the pipe, it was able to self sustain through surface tension and overcome the pressure differential. I also found that I could reliably get water to flow by submerging the other end of the drain pipe.

        My conclusion from this is that when using one of these portable air conditioners as a dehumidifier, one must ensure that water is actually leaving the unit, or else it will be ineffective. There seems to be a delicate balance of gravity and pressure which may need to be overcome by tilting or rocking the unit or submerging the other end of the drain hose in a small amount of water.

        Reply
      • Adding to this, I can also speculate from your picture that the design of the LG models mainly uses gravity to direct condensate onto the condenser coils, and the splasher is just a backup for water that makes it through without evaporating.

        Reply
  4. I’m so glad I found this post, the user manual for my Sharp CV-P10RC did not explain why there are two drains.

    The unit has begun to stop after running a couple hours (after years of running without needing draining). After researching possible causes, I opened the top drain and no water came out. So I got a very low bowl and opened the lower drain. And quickly replugged it because water gushed out.

    Since then I’ve connected a hose to the lower drain that runs to the bowl, and when the pan is full enough it pushes the water up the slight incline into the bowl. But of course, the bowl is much smaller than the pan, so I have to let it fill, empty it, repeat, every couple hours.

    It has been very humid here the last couple weeks, but not a lot more than usual in the summer. Why would the lower pan be filling up like this when running in cooling (not dehumidifying) mode? Might the splasher be malfunctioning and not using up the lower water?

    Reply
  5. Hi Trey,

    Thanks for the great article! I bought a unit like this and it has been incredible. I never had to drain it this summer. As the weather gets colder, I am ready to switch it to heat mode. Which drain plug should I use when in heat mode? I used it a bit last night and the container filled up quickly and gave me an error. I was thinking about hooking up the drain to a condensate pump and pumping it outside. Thanks again.

    Reply
    • Hi Sam,

      Your user’s manual should have setup instructions to run your portable AC in heating mode. However, its most likely the lower drain port that you need to hook up the hose to when using your unit in heating mode.

      -Trey

      Reply

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