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Thread: Cleaning slime mold from condensate drains

  1. #1

    Cleaning slime mold from condensate drains

    I have had both a dehumidifier and a mini-split HVAC unit plug with slime mold already this summer. The mold forms a gelatinous coating in the condensate tray which eventually plugs the drain line. Water spilling out onto the floor is the obvious indication of the problem. For the mini split, the cure is to suck the tray empty using a wet-dry vacuum at the discharge end of its condensate hose. I used a rag around the condensate hose to get a tight seal. Then remove the front cover of the inside unit and fill the condensate tray with a dilute mixture of chlorine bleach (Chlorox) and water to kill the mold. Let it sit awhile then suck it out. Repeat as necessary. I was lucky this time to catch the overflow before any damage was done.

    The dehumidifier (Hisense) has a pump to automatically remove condensate to an outside drain. There is a filter on the suction side of the discharge pump that plugged solid with mucus-like slime. It was gross. Bleach solution and a soft toothbrush cleaned it. The indication of the problem for this brand of dehumidifier is that the bucket fills up and shuts off the unit. Wish the mini-split had the same feature.

    I have had condensate drains at various houses and condos plug before. Routine maintenance is expected, but it takes years of neglect to plug it up. The remarkable thing at the shop was how fast the plugging occurred. We are just half-way through the humid season. The dehumidifier was new last fall. The mini-split had its seasonal service less than a month before it plugged. It has only been in service for less than a year. It was a new HVAC tech who may not have cleaned the drain.

    I suspect that wood dust is providing food to the mold making it grow faster in the shop than in my house. We have also had a record year for pollen and mold in the air. I think it would help to use my air cleaner’s programmable feature to run the filter occasionally when I am not there, change air filters more often, and schedule drain-cleaning twice a summer.

    Hope you all take a moment to pull the front cover of your units and clean as necessary.

  2. #2
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    I have poured bleach in the pipes before. The last time I had my house serviced they (charged me) placed to magic sticks in the beginning of the drain. Hey if it works I am in.

  3. #3
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    I've never had a drain clog that I put these in.

    https://www.amazon.com/Green-Gobbler...dDbGljaz10cnVl

    In our lake rental house, the 1974 kitchen cabinets had that many years of greasy film on them. My Wife tried everything we'd ever heard of, and she finally tried Krud Kutter. That's now our top of the list gunk cleaner. They make one to use with pressure washer pickup. I have some waiting, but no pressure washing job at hand for a while. I'm anxious to try it.
    Last edited by Tom M King; 07-11-2022 at 4:15 PM.

  4. #4
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    I use Krud Kutter in my diamond plates for sharpening. For grease on cabinets I always used mineral sprits.

  5. #5
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    Mineral spirits wouldn't move any of that old stuff, nor would a long list of other normal stuff, even Awesome or Orange Oil degreasers. She left Krud Kutter on it for a while, but not long enough for it to dry, and it almost just wiped off.

  6. #6
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    Look for a Gallo Gun. It is a small holder for a CO2 cartridge with a small tube and a cone shaped fitting. That will blow out the debris so you can then get cleaning fluid out. I think you have traps in the lines. If the water can lay in the line it will and you end up with your problem. This occurs in a pretty high percentage of mini splits. There is a lot going on behind the Ms. power line, Refrig lines and flexible drain line. It all looks good and then you have to close the evap cover onto the mounting bracket. The easiest thing to give way is the drain line.

  7. #7
    Quote Originally Posted by Jack Frederick View Post
    Look for a Gallo Gun. It is a small holder for a CO2 cartridge with a small tube and a cone shaped fitting. That will blow out the debris so you can then get cleaning fluid out. I think you have traps in the lines. If the water can lay in the line it will and you end up with your problem. This occurs in a pretty high percentage of mini splits. There is a lot going on behind the Ms. power line, Refrig lines and flexible drain line. It all looks good and then you have to close the evap cover onto the mounting bracket. The easiest thing to give way is the drain line.
    I have seen one of those. What can you do to prevent spraying dirty water all over the room if the blockage did not clear? The vacuum technique works from outside the house. I have one mini split that drains into a rain gutter way high on the back of the house. I would have to use CO2 to clear it.

    The drain that plugged has a very long hose that goes down the wall, under the floor horizontally for 14 ft and out a side wall. The condensate does get some elevation head from the downward section but flow is so low that any mold that forms will stay in the line until blown or sucked out. I talked to the HVAC tech about ways to drain more directly. It will be difficult.

  8. #8
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    These absolutely changed things for me at work:

    https://aceto.com/Products/Specialty.../CDC-Anti-Clog

    I have 200 or so fan-coil units, and I was always chasing clogged drains during the humid months. Now that I’ve been using these for a couple years, problems have dwindled to near zero. My units are in a high-traffic public building (courthouse), and to say we have hygiene-challenged clientele is an understatement…
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


  9. #9
    Quote Originally Posted by Jason Roehl View Post
    These absolutely changed things for me at work:

    https://aceto.com/Products/Specialty.../CDC-Anti-Clog

    I have 200 or so fan-coil units, and I was always chasing clogged drains during the humid months. Now that I’ve been using these for a couple years, problems have dwindled to near zero. My units are in a high-traffic public building (courthouse), and to say we have hygiene-challenged clientele is an understatement…
    Those sound great and they come in 3/4 oz size that might fit in the mini-split condensate tray. I will check into it. Thanks.

  10. #10
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    Quote Originally Posted by Jack Frederick View Post
    Look for a Gallo Gun. It is a small holder for a CO2 cartridge with a small tube and a cone shaped fitting. That will blow out the debris so you can then get cleaning fluid out.
    I had to use those routinely in my last house. Worked great. Saved a fortune in visits from the HVAC company here in the humidity capital of the World. Though those enzyme products look interesting.
    - After I ask a stranger if I can pet their dog and they say yes, I like to respond, "I'll keep that in mind" and walk off
    - It's above my pay grade. Mongo only pawn in game of life.

  11. #11
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    I have one air handler, with a drain pan under it, in the attic of a rental house that gets the drain clogged about once a year. Not from mold, but from something falling into it. The house is old, and the attic huge. Nothing else is up there. It gets clogged past the trap and I don't even know where the end of the drain line goes. I put a union in the line past the trap. I leave a small ShopVac up there.

    When they call me that the heat pump has stopped working, I go up there, use the shopvac to suck the water out of the now full pan, take the union apart and suck the line out, put the union back together, and take the top off the shopvac so the water will evaporate by the next time I need to do it in another year or so. The people who live there are not able to do that.

  12. #12
    Thanks for the tip, Tom. Bought.

    I have this recurring condition both at home on the humidifier drain, the condensate pump tube, and at work on the furnace condensate drains. I don't think it's unique to a wood dusty shop.

    For the drains, I just friction fit the pvc at a convenient elbow so I can open it in sections and wash them out or buy a new section if necessary. The drains aren't under pressure so the friction fit has worked fine for 20 years.

    I try to use condensate pumps very sparingly, and with minimal tube distance to the nearest drain instead of outside. The less tube, the less to clog. I am not sure this is to code, but it works for me.
    Last edited by Prashun Patel; 07-13-2022 at 4:24 PM.

  13. #13
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    I found some large 1" crystals of copper sulfate and put one in each drain pan. The copper sulfate crystal very gradually dissolves in the condensate and keeps the drain and the pan completely clear of mold and slime. I was doing this for my customers back 50 years ago when I owned a HVAC business, and continue to do it for my own condensate pans today. You will never see mold growing on a roof below copper roof flashing. The same is true there. Copper is a mineral and it's found in small quantities in the earth everywhere, so non-polluting. Most houses have copper plumbing with drinking water running through it. In high quantity, like the crystal, it would be dangerous if you ate it though.

    Charley

  14. #14
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    Quote Originally Posted by Charles Lent View Post
    I found some large 1" crystals of copper sulfate and put one in each drain pan. The copper sulfate crystal very gradually dissolves in the condensate and keeps the drain and the pan completely clear of mold and slime. I was doing this for my customers back 50 years ago when I owned a HVAC business, and continue to do it for my own condensate pans today. You will never see mold growing on a roof below copper roof flashing. The same is true there. Copper is a mineral and it's found in small quantities in the earth everywhere, so non-polluting. Most houses have copper plumbing with drinking water running through it. In high quantity, like the crystal, it would be dangerous if you ate it though.

    Charley
    I love that idea. Unfortunately, my condensate pans are up in the attic, a ladder climb away. Not something I should be doing. I wonder if I could talk the HVAC technicians into doing that the next time they do routine maintenance.
    - After I ask a stranger if I can pet their dog and they say yes, I like to respond, "I'll keep that in mind" and walk off
    - It's above my pay grade. Mongo only pawn in game of life.

  15. #15
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    Charles, Good tip on the Copper Sulphate. Would a piece of copper pipe laid in the pan do the same? The copper sulphate I have is small crystals.

    It's also hard/impossible to get anything to grow below a copper roof too.

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