I have a relatively old air handler that has worked fine for many years. Just recently, it started leaking water everywhere, and it seems to be seeping from inside the base of the air handler itself (as opposed to a leaking pipe, or something outside the unit).

The condensation line that leads outside the house has not had water running through it recently, so that is clearly related. I assume it is backing up somewhere.

But when I pour water into the clean-out, it goes right into the condensation line and outside the house, so I feel like the blockage must be prior to the clean-out. The pipes are glued together, so I'm not able to take them apart, but there is only a few inches of pipe between the air handler and the clean-out, and it doesn't seem to be blocked in there.

Could this be a problem inside the unit itself? Is this something that I could attempt to fix myself? I am moderately handy, but don't know a whole lot about plumbing or HVAC. I would call an HVAC company, but they are all booked several days or weeks out, and I am putting my house on the market tomorrow. I'd prefer to get this fixed before people start coming to look at the house.

I tried opening the panel, but the drain pipe is holding it in. I tried loosening the drain pipe screw, but it won't budge.

Update - Today, the weather was nice, so we turned off the A/C and opened the windows. Periodically throughout the day, I would hear the pump running, pushing water out of the condensation line. So I am assuming that there is a blockage somewhere in the air handler that lets just a small amount of water come through. So when everything is off, the backup of water slowly comes through and gets pumped out, but when it's on, there's just too much water, and it ends up spilling out.

Any help would be appreciated. Thanks!

  • 2
    Have you opened up the unit, and taken a look inside? It's common for small bits of debris to get clogged up in the drain right inside the unit. Without knowing the exact make and model, there's not much more I can tell you.
    – Tester101
    May 20, 2015 at 20:19
  • I attached some photos. The second one is of the specs, if that helps.
    – Robert
    May 20, 2015 at 23:13
  • 1
    If this is an air handler (negative pressure), the drain is installed wrong. The vent (open tee), should be after the trap. As it is now, air can be pushed in through the vent (open tee) and prevent water from draining. This could be part of your problem. The purpose of the trap, is to prevent air from entering through the drain. This setup does not accomplish this.
    – Tester101
    May 21, 2015 at 1:28
  • 1
    If air is coming in through the drain, the water is likely not draining until the unit shuts down. If it runs long enough, the condensate could theoretically overflow the pan. When the unit is running, put your hand (or a piece of toilet paper) over the vent. If you feel suction (or the TP is pushed in), you're going to want to consider replumbing the drain. NOTE: If you're using toilet paper to test, make sure you keep a firm grasp on it. You don't want it to be pushed into the pipe.
    – Tester101
    May 21, 2015 at 1:34
  • 1
    Sounds like it's still clogged. To open it, you need to cut the PVC and unscrew that fitting. I'd cut it right at that fitting that's screwed in (so you can still re-use that assembly). You'll need a new 3/4" threaded fitting, some dope or tape, plus PVC glue and primer (do not glue the threads; use pipe sealant). On newer units, this would be a separate panel.
    – Mazura
    May 21, 2015 at 16:28

1 Answer 1


The Tee was left open as a means of a clean out.

Start by using a shop-vac on that Tee and hold your finger over the other end, in the pump (you may have to get the pump out of the way).

Next, snake it out, going into the machine: (e.g., the brush that comes with an EZ-Trap; johnstonesupply.com)

enter image description here

Followed with another vacuuming. Ideally the first go sucks it out; you don't want to just push the clog inside. If it still leaks after all that, you may have a cracked pan.

  • The tee is left open as a vent, it just happens to make a handy clean out. Just as you have to vent the traps in your plumbing system, you have to vent this trap as well.
    – Tester101
    May 21, 2015 at 1:31
  • I was going to suggest capping it until I thought about it needing a vent, but EZ-Traps don't have an opening (unless it's sneaking past those caps somehow). Am I supposed to putting one in after it?
    – Mazura
    May 21, 2015 at 1:45
  • If you're using one of those things, you could just leave open a cap on the side away from the air handler.
    – Tester101
    May 21, 2015 at 1:57

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