For the life of me, I cannot figure this out. My air handler and heat pump were installed in 2006 and work great. For the first summer since I've owned the home, condensation started to not drain properly and is leaking onto the filter and onto the basement floor. The inside of this handler is spotless, including the drain pan. I took apart the PVC pipe and cleaned it out well, although I don't think it needed it. I still have major dripping!

It does not look to me like it should be overflowing. It pours out of the hole circled below and then onto the floor and back into the unit and onto the filter. If it is coming out of this hole, why is it not going down the correct outlet to the pipe?!

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The only change point I can think of is that I purchased a box of filters on the web that had a pretty high MERV rating of 12. The fan seems to push air through it pretty easily, but I am wondering if this is somehow producing a vacuum that is not letting the water drain correctly. I removed the plugs pointed out below by the arrows to try and relieve this vacuum, but it did not work. Any thought or advice?

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Last night, I cracked open a cold one and just watched in the basement. I can here the water build up in the pan as it makes this gurgling sound like some force is preventing it from draining, but it is on the verge of overflowing. Once the blower stops, all the water drains quickly. Some down the pipe, some out of the that hole. If the water is building up, I simply don't understand why it won't drain down the pipe.

The water also drained when I removed the filter and left the cover off while the blower was running.

  • Try using one of the older filters, and see if the problem goes away. If you've added restriction to the air flow, the coils could be icing up. This would release a larger volume of water at once (when the ice melts), instead of a steady stream (as the condensation drips). Could just be that the drain is being flooded. – Tester101 Aug 26 '14 at 14:09
  • I forgot to include this in my original post. I thought that removing the filter entirely would solve the issue and I tried that. It worked at first, but then yet again, water would still spill out with no filter. It wasn't as bad, but it still happened. – Evil Elf Aug 26 '14 at 16:05
  • Have you checked the refrigerant level recently? Could be that you're under or over charged, and the filter magnifies the problem. Have you made any other changes to the system (closed registers, blocked returns, etc.)? – Tester101 Aug 26 '14 at 16:11
  • I've always had about half the registers on the first floor closed (two-story home) and it has never given me a problem before. I updated my original post as well. – Evil Elf Aug 27 '14 at 12:32
  • Sounds like it's sucking air in through the drain, which I would think is because there's not enough return air provided through the return intake. If the system works fine without the new filters, but has problems with the filter. I say stop using those filters. – Tester101 Aug 27 '14 at 13:04

What you’re describing sounds like a combination of negative pressure in the compartment that the drain pan connected to and an incorrectly sized p-trap on the condensate drain.

The depth of the t-prap has to be greater than the negative pressure in inches of water column of the compartment where the drain is connected to. A t-prap with insufficient depth, will prevent the condensate from overcoming the negative pressure which prevents draining until the fan stops.

Further information on sizing of p-traps for condensate can be found in this pdf article: Condensate Traps by Ronald F. Brusha.

  • I don't have a P-trap. Could that T joint be an issue? The pipe is sloped every inch of the way to the basement floor drain. I have also tried to remove the entire pipe drain and just let that first 90 degree piece empty out onto the floor. Same results. Could it be that I NEED a P-trap? – Evil Elf Aug 27 '14 at 17:37
  • If the compartment has a negative pressure, you should have a p-trap. – pdd Aug 27 '14 at 19:20
  • I think this is the case. I will try to correct. How could this be installed incorrectly. Could the handler be more powerful than the return vents are originally designed for? – Evil Elf Aug 27 '14 at 19:33
  • Your best bet is to look up your unit on the manufactures website and find the installation manual. It should include information on how to size the p-trap to account for the unit's operational pressures. If they don't explicitly detail the p-trap, you should be able to get the operational pressure and use the article I linked to to get the dimensions. – pdd Aug 27 '14 at 20:01
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    @Tester101, The trap is not to prevent sewer gas in this application. It's purpose is to maintain separation between zones of different air pressure while allowing the condensate to drain. – pdd Aug 28 '14 at 15:42

I had the exact problem with my condensate drain not draining while running. My unit design is such that the blower pulls air through the A-Coil rather than pushing it through. This design pulls air through the drain pipes and won't allow water to drain. Typical drain configuration utilizes a Tee with a stand pipe so the drain is open above the trap. This is fine if your system pushes air into the A-Coil. However the negative pressure or vacuum of my system requires that you cap off the stand pipe so that air cannot flow into the drain pan housing disrupting the gravity flow of the water. Instead, allow air to enter the drain pan through the secondary drain port. If this scenario pulls water out of the trap, consider installing a larger trap. Worked like a charm, high and dry now!


I know its a little late but I had a similar problem and my coils were stopped up with dirt. I cleaned my coils with coil cleaner and a tooth brush and rinsed with water. Make sure you brush with the grain on the coil so it doesn't get damaged. Then rinse with water. I repeated this process 3 times because it was so dirty. I used a pump up sprayer to rinse. Lol. After cleaning the coils everything is running smoothly.


Not sure where to put update mods...

Here is my setup after correcting. I started getting overflow again and I reread the thread. I had the clean out above the trap open. I capped it with the threaded fitting and it immediately started to drain again. I'll post back if this is not a permanent solution. I made the trap one inch longer than the installation manual stated.

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I can assume that this has been fixed by now being as that I am 2 years late, but I'll answer this anyway, that pipe on the left doesn't need to be there at all it serves no purpose (normally it is used on units that sit on their sides and have an external secondary drain pan) just put a cap on it and forget about it. The one on the right is built wrong. The vent that you see on your drain (the part sticking up that is open to the air) should be on the other side of the trap not between the trap and the unit. Easiest way to fix is just call a local HVAC tech and have him fix it we will have those parts on our trucks if not we know where to easily get them. If you don't want to go that route just go by home Depot and buy some 3/4 PVC, a male adapter, some elbows, one tee and some PVC glue. You will have to cut out all of that p-trap and rebuild it with the vent on the other side on the trap don't forget that the vent needs to end higher than the hole leaving the unit.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Aug 21 '19 at 10:21

I had a problem last year starting in May, 2016. The Goodman AVPTC4260 air handler had been installed new in the summer of 2013, along with my heat pump. We did unit installs, with an HVAC friend, who installs and maintains Goodmans for a living, handling that end of the job.

Starting in May 2016, I went through 3 motors in 3 months, not including the original one. The moisture was not draining properly even though the filter was cleaned according to the same schedule I had maintained for the 3 previous years. The drainage pipe was never clogged.

My air handler is mounted horizontally in my basement. This unit is designed where the drain pan is directly below the motor and it seems, the "pull" on the motor was so great that it was pulling the water back into the motor and flooding it out. These motors cost $450 each and each lasted a month. I replaced in May, and then surprise - the same problem occurred again in June; at that time, we had a larger pipe installed. Then this happened again in July. With the 3rd motor, I purchased, we had a second drain installed. This seems to have solved the issue.

[Refer to your installation instructions with regard to mounting, because there is a section on motor orientation, water collection and possible motor damage. This was not our issue,]

As a side note, we generally vacuum out the filter every month. I have 2 filters, one gets installed, one gets vacuumed and washed in warm weather. I think you should find your own perfect duration for filter maintenance, as it really does depend on what you do in your house. Pet fur is a great "binder" for dust and sawdust clogs filters fast. Moisture can sit in the dust then and not drain. We were turning off the HVAC when my floors were being redone last summer, so that the inordinate amount of dust did not cause a problem. It was August, so I got the house nice and cool, then turned everything off. The filter was vacuumed more often during this home project, as we never put our finger on what caused the May - July problems. The only thing I could think of was, it was humid and the water was accumulating faster. We were generating more dust, but we were cleaning the filter more often. Anyway, everything has been fine since the second drain was installed.


I just had a similar problem. Unit worked well for two years but then low pressure fault and water leakage when the fan shut off. Turned out there was negative pressure that prevented draining. Sucked air in through the drain hole flooded cabinet and water leaked when fan shut off. Cut in additional cold air return and solved problem. Unit must have been right on border of low pressure fault and pressure sensor weakened over time. Unit was a geocool geothermal 5 ton. I have had good luck having it 5 years.

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