How to clean the circulation lines on your boat air conditioner or refrigerator

With any boat, there comes a bucket of maintenance to be done at all times.  One of the easiest and most beneficial ones you can do it maintaining your air conditioner water circulation lines if you live aboard your boat in the south.

I know there are purists out there that don't run the A/C and certainly if I were anchored off a beach with a nice breeze, I wouldn't be either, however we are not right now, we are living aboard at a dock and it is summer in Louisiana.  That means we want air conditioning and we want it cold and we want it always :)

As most of you know unlike a home, a Marine air conditioners doesn't have the large unit outside like a home that has a fan and air cools itself.  Nope, instead the marine air conditioners are water cooled, they pump whatever water your boat it in, through the system to cool it down and discharges it back over the side of the boat.  That means that the lines are subject to any growth be it marine or plant that may grow near you to grow in these lines.
All of these systems have water strainers to keep grass and what not from entering the pump, but small particles and allege still do form and take their toll on the lines much like cholesterol on the human arteries.

About every 2 years we flush out the lines of the air conditioners.  To do this, we mix up about a 20-25% solution of muriatic acid to water and put it in a milk type jug or jar to make it easy to pour.  I have heard of others that use vinegar to do this but we almost always have the muriatic acid on hand for the treatments we do for the electrodes in our waste treatment system, so it is easy enough for us to use this.

The best way to prep a boat for doing this and other maintenance to the water circulation lines is to install a tee fitting just between the pump and the water strainer that has a valve on it.  This allows us to put the solution in very easily and we just keep a small piece of hose with a screw in fitting for the 2 on one end and a funnel on the other.  See video to show how to assemble and connect it.

In short, we use vise grips and clamp the water line between the entry point and the pump and connect the discharge side of the vacuum to it and blow out until we hear air coming out the seacock on the bottom of the boat (the water intake side).  We close the seacock, then remove the vise grips which blows all the water out of the line from that point to the discharge side.

Then we tie the funnel up higher than the highest point in the system and slowly pour the acid solution into the lines and let gravity carry it through all the coils.  We do this until we see it come out the discharge side of the boat   We now know on this boat it is about 3/4's of a gallon of fluid so that makes it easier on future clean-outs for this boat.

Once the lines are completely full (and you have seen some water come out the discharge you know that all the lines are full even the high spots.  Then just let the material sit in the lines.  I never let it sit for more than 45 minutes and typically I plan for 30 minutes.  One of the things to be cautious and aware of is that the lines in the air conditioner unit are copper and the acid could damage them if it is mixed too strong or sits to long.

After pouring the mixture in and letting it sit, it is then time to neutralize any acid in the line.  This can be done with about a 1/4 cup of baking soda mixed in water.  I just pour a gallon of this through the lines as well and this neutralizes any of the acid in there.  
The last step is to blow the lines clean again with the discharge side of the vacuum and look at what comes out, you will be pretty amazed.

Then it is just connecting everything and starting up the circulation pumps again.  All good for another 2 years or so.
The frequency you may have to do this is dependent on what kind of growth you see.  In my case, we are in a nice little hurricane hole, but we are in a river just up from brackish water so it is primarily fresh water and we get a lot of algae in the summer that grows in the lines.

I hope you find this helpful for any work that you need to do as well on your system.  Again this is a pretty easy job and the hardest part is the first time installing the tee to the line.  I found that having the tee allows me to bleed air out of the system, test flow, it is kind of cheap alternative to a bilge pump in an emergency situation in that I could connect a line from that tee to the bilge and shut off the inbound sea-cock to increase pump capacity.  There are tons of reasons why the tee with valve is handy to have.

Take a look at the picture to the left, you can see the brown stuff in the water, this is all of the gunk that was cleaned out of the lines from the acid flush.  This water is already pretty brown where we are, can you imagine if it was not what this may have looked like.

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  1. My apartment is positioned in a way that the sun shines though it for the whole day.It is extremely hot. I'm considering buying a new AC from website, cause this heat kills me inside. So, your tips will be useful for me soon:)

  2. Thanks for the comment Ashley but unless you are going to plumb a water cuculation line in your apartment, this solution won't really apply to you.
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    Thanks again.