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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 04-06-2009
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Converting window AC to Marine AC

Yep, I'm ghetto! But none the less I'm $54,000 in debt for engineering school so I am going to use it.
I have marine AC on my boat but it's 16500 btu and a honda 2000 eu may not be able to run it. So I have a back up plan.
I have a 52000 btu window unit. I have taken the cooling fan off the condenser side and I am going to bend copper tubing and put a coil against the condenser and run sea water through the copper coil. I am going to box the heat exchanger in and possibly add oil to aid in heat transfer. I would use stainless tube but it's very hard to bend and I don't have any.

My question is this to all the smart guys on here; will the copper tube I bought at home depot hold up or will the sea water eat right through it?

I can chrome plate the copper tube if necessary, is that a viable solution?
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Old 04-06-2009
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you are going over kill. sell the 16 k air and get a 9 or 10 k portable air conditioner this one and find some where to put it, then run the exhaust hose to a port or make an insert for a hatch

edit use the degree to make an adapter for flexible duct like for cloths dryer with dampers so you can just cool the area you need at any one time

Last edited by scottyt; 04-06-2009 at 09:58 PM.
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Old 04-07-2009
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The problem with units like that is they are pulling air from the cabin to exaust the hot air. It makes them very inefficient. Also they may dispell humidity from the air they cool but they bring in that much more humidity in the air that's rushing in from the outside to fill the underpressure they create.
I just bought a window unit for my shop apartment. I was going to buy one of those until I read a bunch of reviews.
The only one's like those that would work well is the ones that bring in air from outside, cool the condenser and then exaust it back out. Those are very expensive. Plus I'd have to cut holes in my boat or rig up something else and I still have to deal with hot air some how somewhere.
I really like the idea of converting a compact unit into a marine unit. I just am not sure of the metal I have to use to do it.
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Old 04-07-2009
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The simplest solution is to make a split drop-board with a cut-out in the lower section sized to fit a window AC unit. On a Catalina 30, you'll also need to add a small support to the outside end of the unit to help support it.




A $280 6500 BTU window unit from Lowes should be quite sufficient. See Frigidaire at Lowe's: 6,500-BTU Window Room Air Conditioner . If your unit is like the above, the drop-board solution will do the trick.
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Last edited by svHyLyte; 04-07-2009 at 08:34 AM.
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Old 04-07-2009
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Copper tubing is much better than stainless in sea conditions. stainless might give up if the covering oxide layer is gone.
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Old 04-07-2009
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Hermit

Hermit,

Air designed units are just that air designed. What you are trying to do is create a HX type unit which to do properly needs proper flow characteristics, a circulation pump, and among other things a totally sealed & submerged evaporator. The condenser needs to be in air to condense and remove humidity which is part of air conditioning.

It's a nice idea in theory but one that won't work for for very long. Perhaps you could find a water cooled evap and solder it into the existing unit then recharge it but then of course it all needs to be balanced and that will be tough to do sorting through dumpsters for the right parts..

Have fun playing with this but in the end you'll wind up getting the properly designed unit and wasting a perfectly good window banger....

P.S. Why not test your existing 16,500 btu unit on the Honda EU before assuming that it won't work. If you can get beyond the start up load you should be fine..

Oh yeah and copper is very durable in sea water though it does tend to turn green. Most engine HX's are made with copper..
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Old 04-07-2009
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Thanks for letting me know about the copper.
I am not versed on matching condensers an AC units to the existing compressors, expansion valves and evaporators, so I need to leave the recirculative evaporative units original and intact.
From what I understand it's the evaporator that removes the humidity from the air. The air hits the cool surface and the water vapor condenses and it runs down into the tray, back to the condenser area (which is outside of the living space and hot) and then it drains out or in most new units part of the condenser coils are in the drain tray and evaporate the water so there is little or nothing to drain.
I am going to drain the liquid condesate into the sink drain through hull.
I already have a seawter pump, through hull, and strainer set up to run seawater through the copper tubing.
I have come up with a lot of ideas that seem rediculous. But trying them out and making them work is part of who I am.
I will run the 16500 unit until it dies. I am going to get a honda 2000 if it runs that one or not. I hope it does.
Thanks again for your help.
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Old 04-07-2009
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Scott, I'm sure you can put that engineering degree to work and figure this out.

You're right, Maine Sail got his terminology backward about the evap and condenser. I catch myself doing that all the time. To make a water cooled condenser, all you need is the right length and diameter copper tube submerged in water. No rocket science there. Figure out how much tubing you need by looking at the original condenser, then coil it as small as possible without cracking it. Silver solder fittings on the ends that can pass through (and seal to) a pvc cap. Put a pair of hose barb fittings in another cap, with one having a length of tube on the inside as well to reach the other side of the heat exchanger. Shove the whole mess inside a pvc pipe and solvent glue the caps on. Mount it well above the water line and plumb it to your water pump and a/c lines. You can use the a/c condenser fan motor leads to run the water pump or a relay for the water pump depending on the amperage of the fan vs the water pump.

I wouldn't tie the condenser drain to your sink drain. The condenser is just a catch pan and unless it's mounted well above the water line (even when heeled over), you're asking for trouble. Instead, I would drain it into the bilge, and let the bilge pump take care of it.

BTW, if you want to find some pics of a heat exchanger built this way, surf some salt water fish tank sites. search for DIY chillers. The only difference is that a fish tank chiller submerges the evaporator instead of the condenser. Fish tank chillers also use stainless exclusively because leaching copper into the water kills (very expensive) invertebrates, just like bottom paint.
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Another option for this sort of thing is to find a way to circulate air to the existing condenser. On my boat, I have a window unit that sits under the companionway stairs where the engine used to be. I built a fan shroud for the back of the unit and installed 4 inch dryer hoses to the cowl vents that were already on the boat. Booster fans were needed (good ones, high flow rates, not the ones you get at home depot) to get enough circulation. The condenser draws air from under the cockpit, which is fed by the cockpit lockers and exhausts out the cowl vents. The evaporator draws air from the cabin and blows out cold.
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Old 04-07-2009
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Watch the level. Many ACs don't tolerate tilt.

If they do, it is in one plane but not the other. It can also cause the compressor to run without lubrication.

When in doubt, don't run it underway. You should not need to.

Mainsail was right about trying the generator first; I know a fellow who runs a unit that size on a 2000. The inverter carries a part of the load using the batteries for about 10 seconds, then it is fine. That's what hybrids do. Check the inverter rating, contiuous and surge.
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