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Cleaning A/C drain line?

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  • Cleaning A/C drain line?

    After driving all the way home with a screaming baby in the back seat, I come home to a hot house. Immediately check the float valve, sure enough, drain filled with water. After getting both kids in bed, I drag out the extension cord, shop vac, and garden tractor to provide light and begin sucking the line. I think everything is cleared up, so I pack everything up and head back inside. 10 minutes later, A/C stops again, same problem. Ok, I am a little bit pissed at this point, but living in Florida, I suck it up and do it all over again. This time I use tape to attach the vacuum hose to the drain outlet, leave the vacuum on, and go inside to the float valve and start to pour bleach down the pipe. I found it strange that there wasn't as much suction on this end... Ok, I wrap it all up and 10 minutes later, it stops again. I now think the main drain pipe is not the issue, but the junction where water can go to either main drain or float valve. Well, I elevated the float valve tube and it quickly drained... I left the damn thing elevated, disabling the float valve. I'd rather have a potential wet tile floor than sweat all night.
    So, I am thinking of rigging up an adapter to use my air compressor to literally blow the sh1t out of the drain pipe from inside the house. Thoughts? Will it break something? Everyone on YouTube regurgitates the same crappy vacuum way.

  • #2
    Lot's of guys like to use a "Gallo gun" because they are easy to carry up into a house with an attic air handler. Uses standard 12 gram bb/pellet gun CO2 cartridges. I just use a blow gun with a rubber cone on the tip with my Nitrogen tank. Just don't go crazy on your air pressure and use quick bursts and you'll be fine.


    • #3
      Float valve on an AC drain line? That's new to me. Sounds like they out-smarted themselves.

      When I lived in Florida I had constant problems with the AC drains. The unit was in the middle of the house and the drain line was around 20 feet long. I finally added a drip loop with some clear, flexible tubing. The clear tubing allowed me to see when it was clogging up. I was in the indoor unit, just outside of the evaporator coil and I attached it with hose fittings so I could clean it out. AND, I could attach a hose to it and blow out the drain pipe with full city water pressure. That worked great!

      But I don't know about a float valve. I guess that takes the place of a drip loop to stop hot, outside air from coming into the house. And critters too, I guess.

      I had a new AC unit installed in my present house a couple of years ago and there is no float valve.
      Paul A.
      SE Texas

      Make it fit.
      You can't win and there IS a penalty for trying!


      • #4
        I'm a plumber and we typically leave that to the HVAC guys, but I have blown one out with a nitrogen tank. I have also run a tiny auger (the type that mounts a small drum of cable onto a drill) into one to clear out buildup. After you get it cleared out, use enzyme cleaner for maintenance. It's a living organism that digests organic material. It should prevent clogs in the future.


        • #5
          Float valve = Float Switch, when the line fills with water, it turns off the A/C unit.
          Well, the A/C ran all night, and the drip line is clear! Will check out the Enzyme cleaner


          • #6
            Condensate pan tablets.

            Just one of many similar products.


            • #7
              If your situation allows, relocate trap to outside of house at ground level. Don't glue the trap joints. You will now have a self flushing head of water behind the trap and it will not plug up nearly as often. When it does plug it is easily cleaned. Pan treatment is a good idea but bleach is not. Power flushing will help if drain line is not properly pitched / supported and has bellies or a series of traps.


              • #8
                For attic mounted units, the water heater is usually nearby. Put a female garden hose connector on the condensate line vent pipe if you have one,( if not put a Tee in the line upstream of the trap) and install a ball valve in the drain line between the trap and the A/C unit. Run a garden hose from the water heater drain faucet to the hose connector. Close the ball valve. Open the water heater valve and blast the entire drain system with hot water. Every couple of years is usually adequate.

                Last edited by RWO; 06-18-2017, 02:10 PM.


                • #9
                  All the float switches I've seen are on the emergency pan underneath the whole HVAC unit.
                  There are two drain lines going outside. One from the inside HVAC pan in the air handler. That's your normal one and it typically has a trap right out of the air handler.

                  When that one clogs up the water starts leaking out of the lower seams of the air handler and the emergency pan collects it. Some pans have a 2nd drain to the outside. Some don't.

                  The float switch is on this emergency pan so it can't overflow and ruin floor coverings. If it's in the attic it stops the water from overflowing and wetting the ceiling below. The float switch interrupts the low voltage controls and the HVAC compressor won't run. The fan in the air handler may continue to run.


                  • #10
                    What causes the clog may be different in your area. But, in So. Florida typically there's an odd mineral-like deposit that forms in sticky flakes. My AC guy uses lye to clean it out. BUT be careful, lye eats aluminum, it needs to go into the PVC drain pipe only. I have used a hose adapter attached to a piece of PVC pipe that fits into the opening where the float valve goes, to gently flush out the residue. Too much pressure could be a problem, the drains (at least the ones I have) weren't designed for pressure....


                    • #11
                      It seems once a year this crops up, believe its algae