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  1. #1

    Condensate Drain Line Mystery - opinions?

    Hi all,

    The condensation from my central air handler has been running through the secondary drain line and into the secondary drain pan (below the unit) for quite some time. My husband and I initially thought that the primary line was clogged, but this does not seem to be the case.

    Here are pictures of our unit:




    We had an HVAC technician come out to perform basic maintenance (including flushing out the drain lines) a month ago. He's convinced that we've got mold and mildew growing in our coil box and drain lines (and growing so fast that it's re-clogging them even two weeks after his visit). However, a certified mold inspector was adamant that this wasn't possible.

    I don't think the primary line is clogged because you can feel strong airflow through the pour spout when you remove the cap (and you can hear it when the AC is on in a bathroom sink).

    I opened the coil box yesterday, and there was some mold/mildew along the material above the evap coils, but none on the upper/outside portion of the coils (we have an A-frame with a plate blocking view of the inside portion of the coils and fins). I sprayed liberally with fungicide (rated for HVAC system use) and closed the box.

    There's no trap on the primary line, the pour spout hasn't always been capped, and air escapes from the coil box around the panel and the front seam in the duct work immediately above the coil box (I've sealed this with foil tape for now and will add sealant later).

    Given that the primary line doesn't seem to be clogged, the most likely (and frustrating) explanation seems to be that the unit wasn't installed well. You'll notice that the primary and secondary drain lines connect to the coil box at the same height, so someone would have had to add just the right slope to the unit or primary drain pan to keep condensation flowing through the primary line. As it is, I suspect that water flows freely through both at the same time.

    I'd appreciate any help or insight. Thanks!

  2. #2
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    1,768
    There is likely a weir dam around the overflow drain inside the unit to make sure the primary flows out first. If gunk has built up enough around the primary inlet, or if the weir has eroded away, you can possible be sending it out the wrong one... Of course, it's also possible that they are in fact isntalled backwards, and the primary is actually the drain on the right hand side. Not knowing that particular unit would be hard to say one way or the other.

    Also, a trap really should be installed - no sense air conditioning the bathroom through the stinky drain line... It's really cheap and easy to knock together a simple trap. I can't believe the AC guy didn't try to sell you on at least this simple work.

  3. #3
    Join Date
    Jul 2004
    Location
    Massachusetts
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    6,837
    From here it looks like both drain holes are at the same level. That being the case, there should be a secondary plastic panel behind the PVC adapter through which a hole smaller than the main drain is drilled to require the drain pan water to reach a greater depth before the water exits through the secondary drain. Are you sure there is no water exiting through the primary drain? I'd request that the HVAC tech verify which is primary and which is secondary before jumping to conclusions that something drastic is wrong.
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  4. #4
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
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    Looks like a hack install to begin with. Maybe there is a trap in the line somewhere? Is the end free and clear? What comes out of the primary every time the tech blows it clear?

    Better replace that emergency drain pan soon or you'll be having bigger problems...
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  5. #5
    Join Date
    Jul 2006
    Location
    Virginia
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    4,619
    Looks like they could have the lines switched

  6. #6
    Join Date
    Feb 2008
    Location
    Waffleville
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    10,339
    where does it terminate? is that free and clear?

    wet dry shop vacuum applied at the right place could free up the drain line.... if i where an enterprising person that's what i would do...

    also.... that coil, when dirty... will allow condensate to drip straight down into the furnace and not allow it to run into the drain pan, in your installation (the pictures you've posted)

    so you may also have a dirty indoor coil, drain pan, and a dirty drain line.

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  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    If the supply air static pressure is on the high end, it is common for water to be blown out of the drain pan into the secondary drain when the pipe is completely open like that.

    If this is the case, which it often is, the ultimate solution is to fix what is causing the high static pressure, usually it is a restrictive duct system, or to high of a blower setting.

    There are a couple of things you can try as a quick fix if you have determined that the primary drain is clear, and water is draining through it.

    If you leave the cap off the vent stack in the primary drain, you may find that the water level in the coils internal drain pan will run just a tiny bit lower, and may prevent water from being blown out the secondary outlet.

    A trap in the secondary drain will stop the airflow out the drain line once it gets enough water in it to make a good air seal, and will prevent more water from being blown out the drain.
    A cap with a 1/4" hole in it on the end of the secondary drain, where it ends at the emergency drain pan, often will slow the airflow through the pipe down enough to keep water from being blown into it, but still allow drainage if the primary drain becomes clogged.

    I see this kind of thing quite often when the humidity is high.
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  8. #8
    Thanks for the help, everyone.

    beachtech--I can't see where the primary terminates because it appears to feed into the house's plumbing/drainage (which is why we can hear air in that one bathroom sink when the AC is running), so I can't shop-vac it (but we did get it cleared with compressed air when the technician came). As for the coils, I sprayed them with cleanser when I opened up the box the other day, but the parts I could see looked pretty clean.

    I found out yesterday that this drainage problem has literally been happening since my husband bought the house. As a first-time homebuyer, he didn't know that the big pan below the air handler wasn't actually supposed to collect water or that it was a bad sign if the outlet connected to it was draining (and I wouldn't have known that back then, either). This makes me almost certain that it really was just a bad installation job, and it's just a shame that we've only learned about this so late.

    Thanks again for your comments!

  9. #9
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,975
    Quote Originally Posted by CLP View Post
    Thanks for the help, everyone.

    beachtech--I can't see where the primary terminates because it appears to feed into the house's plumbing/drainage (which is why we can hear air in that one bathroom sink when the AC is running), so I can't shop-vac it (but we did get it cleared with compressed air when the technician came). As for the coils, I sprayed them with cleanser when I opened up the box the other day, but the parts I could see looked pretty clean.



    Thanks again for your comments!
    Your drain does not terminate correctly. Having a tech fix where it drains to, to a correct location, will most likely solve the problem.

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