We have a central air conditioning unit that has one part of the unit in a closet. The blower connected to the ductworks and coils in this part of the unit, while outside there is a compressor and blower unit.

There is a rather long PVC drain line from the indoor unit to the outside. There is a catch connected to the drain via a small hole which opens up into larger PVC, which then goes down into the floor, and comes out about 6 feet lower on the outside of the house, where it then goes down another run of PVC to the yard.

The issue is that periodically this rather long piping clogs. There is not a large amount of catchment at the unit itself, and there is no indication if the drain is clogged, so it fills up and then starts overflowing into the intake vents space below the unit and the eventually works its way to the flooring where it proceeds to cause damage to the wood, causing it to curl upwards.

I am not sure what to do about this. When it happened the first time I was able to clean the drain line by attaching a vacuum to the PVC outlet, and then flush more water (by carefully pouring it into the catchment area and waiting for it to drain) until I was pretty sure it was cleaned out. There seemed to be some green stuff suggesting some kind of biological buildup, so I also flushed some bleach down, and have been pouring bleach down monthly.

I was not, however, able to figure out what to do about the damaged part of the floor. The local flooring store was not able to tell me anything - I took a sample of the flooring and they were clueless aside from redoing the whole floor with something completely different. I tried looking for handymen on Thumbtack but didn't get any responses from my inquiries that made me confident in wanting to let any of them come out and look at it. At the time only about 2 square feet around the closet were damaged, part of it under the door. I do not want to replace the whole hardwood floor (it's in a hallway adjoining two bedrooms and is wall to wall hardwood in the whole thing) so nothing was done.

Now however, despite the monthly bleach regiment the unit has backed up and overflowed again, this time damaging around 6 square feet of flooring. There was no green in the suctioned backup this time, or any obvious gunk, although it was a bit dirty looking (this could have partially been due to remaining stuff in the vacuum from a previous cleaning).

I have two questions:

  1. Why does the blockage keep coming back? How can we prevent it from coming back since it is so hard to spot and damaging when it does?

  2. How can we repair the flooring? I have tried prying up the loose wood, but the parts that are not wet are very securely glued and I don't know how to detach them without making a big mess (breaking the piece, leaving lots of remnants stuff attached which I have to somehow remove).

Pictures: 1. The floor in front of the air intake. The grate has been removed, as well as the flooring that would come up. enter image description here

  1. The floor near the hinge of the door of the utilities closet. enter image description here

  2. View of interior showing catch (black plastic) and exterior piping leading away from unit. enter image description here

4.Closer view of catch, including opening to PVC piping. enter image description here

2 Answers 2


The drain pan should have a limit switch/sensor which prevents operation of the unit if the sensor detects the pan is full. Either this switch/sensor has gone bad or was never installed to begin with. I've never installed/replaced such a sensor so I cannot state how hard it would be to do so, but my guess is it should be fairly simple.

The condensate is not pure water. Sometimes it can seem more like syrup--at least that is what I have observed. There are various options. Periodically adding vinegar is one option. Bleach is not recommended. Note, you can also have this issue in winter if you have a high-efficiency condensing furnace. You definitely should clean the drain out bi-annually. Quarterly would be better....

If it were mine, I would probably rip out the flooring and replace with tile or vinyl depending on how visible the area is and how often it is accessed. This flooring appears to be some type of cheap laminate (read that: not worth trying to fix) in my humble opinion.

Read more here: https://www.artplumbingandac.com/air-conditioning/how-to-unclog-an-ac-drain-pipe/

  • sadly, nearly the entire level is covered with the laminate stuff and replacing all of it isn't really doable at the present time...
    – Michael
    Commented Sep 30, 2019 at 18:49

The diameter of that drain pipe looks like you could snake it, which in my experience is the best way to actually clean/unclog a pipe. I'm not sure if you can get access to the other end where you can run the snake without cutting the pipe, but there are a few 90s at the end in the photo, so you might need to do both ends. I do think the other person was right though; twice a year is probably about right. Also, I agree with their advice to put tile there, but if you're worried it'll look weird or you're not up to the job you could just cover it up with a small mat or carpet.

  • Ok so... the PVC actually isn't welded on its final run once it exits the house, so I can put the snake right in with one 90 degree turn before it enters the house. But - I am having a terrible time getting it to go around 90 degree turns at all. I managed to get it past the first turn immediately after entering at the elbow, but at the second turn it wouldn't go any further, and coming back out I feel like it almost got stuck just on that initial bend. On this inside, I couldn't even get it to get around the first bend. This is what... 3/4" on the main part and 1/2" on the first elbow?
    – Michael
    Commented Oct 1, 2019 at 0:57
  • Is it welded by the floor near the furnace? You might have already tried that, but if you could get at it right before it goes into the floor I wonder how much of a straight run it is. You could also try a different type of snake, maybe a fish tape like electricians use and see if you can get further. Or, Perhaps you could try another approach. I purchased a condensate pump for my in-law's air-condition off of amazon for about 60$. Could you simply install the pump and run the line to a nearby drain or window? Installation was super easy.
    – Steve
    Commented Oct 1, 2019 at 17:52

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