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How To

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AC Condensation Tube Clog

Most everyone knows that when you use the air conditioning (AC) in your car a puddle of water will form under the vehicle – water is a normal byproduct of the air conditioning process.

The same is true for the air conditioning in your home. The difference being that for home AC units (we're using central air as an example) this condensation has to be routed away from the interior living spaces and exits the home through some sort of drainage system.

In addition, bacteria forms inside the AC drainage system (it looks like algae) and can cause the drainage pipe to plug up. If this happens the condensed water will back-up inside the AC unit and begin leaking in and around the unit. The leaking will continue until either the AC unit is switched off or the plugged-up pipe is cleared. Home AC units are capable of condensing and expelling many gallons of water in a relatively short time period and this problem was identified as a potential risk within this home.

With some design-work complete and about $12 worth of plumbing parts in-hand we're ready to work on this interior AC unit. The goals of this project are to minimize the risks of flooding and provide an easy way to clear the pipe if it becomes clogged with bacteria. We're going to rely on compressed air to do the job for us since snaking the pipe out sounded like a horrible job on a good day.

pipe overview

This piping has already been replaced once and a water trap was added to prevent sewage gases from backing up into the condensation pipes and entering the home. (A) The water exits the AC unit here and travels to (B) where it attaches to copper plumbing, enters the slab foundation and connects to the sewage line. (C) is a vent tube and (D) is the water trap.

pipe orientation

Through the magic of photography we've added a valve (E) that we can open and close and this enables us to isolate the AC unit from the rest of the condensation plumbing. If we tried to clear a clog without the valve in place, compressed air would escape into the AC unit and we'd never build-up enough air pressure to clear the clog. With the valve in the open position condensed water vapor is able to flow through the pipes and out of the house just as before.

blow gun and gasket

The vent tube is where we'll shoot the system with compressed air and we'll use a blow-gun that attaches to a compressed air line to do that. We found a soft rubber washer in the Dirty Shirt shop that slips over the end of the blow-gun and this will provide a tight seal to the condensation plumbing when we give it a shot.

blow gun and washer

Here's the blow-gun with the soft pressure washer installed.

blow gun attachment

We've turned the AC unit off to stop the flow of condensation into the clogged pipe. The valve has been closed (F) enabling pressure to build in the pipe that will blow through the clog. The blow gun and washer are pressed onto the vent tube (G) and a few hits of air pressure are applied until the clog clears. The compressed air line is not shown in this photo to make it easier to photograph in this tight space.

We're sure that there's a maximum pressure that would cause the pipe assembly to burst but we're not sure exactly what that pressure would be. We're using about 80 pounds of air pressure to clear the clog. If you have really old pipes or other worries about performing this procedure then back down on the air pressure and work your way up incrementally until the clog is cleared.

funnel shot

The final step in clearing the clog is to install a funnel and pour a 25% bleach / 75% water mixture into the pipe. The bleach will kill the bacteria and cause it to release from inside the pipe and wash away. Repeat this process several times to be sure the pipe is clear.

finished photo showing valve

The clog is cleared, the bacteria have been washed away and the job is complete. Remove the funnel, open the valve and turn the AC on.

At one point we had an AC repairman tell us that the water trap was installed in the wrong position for this unit. Our experience has been that it works well and therefore we'll leave it just the way it is.

This house is located in a warm climate and the AC unit runs almost non-stop for most of the year creating a lot of condensation/bacteria. We also know that for newer home construction builders use a larger diameter pipe to route condensed water away from the AC. The larger diameter pipe should dramatically lessen the chances of a clog and so would using the AC less often in a cooler climate. Since this house is built on a slab foundation it is completely impractical to entertain replacing the existing pipe with larger pipe. The cost and mess would be significant. The Dirty Shirt crew is familiar with jackhammers and concrete foundations – run, don't walk in the opposite direction. The solution for this home is to continue cleaning the pipes with bleach and water at three month intervals to avoid clogs before they occur; all for about $12.