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Old 07-09-2013, 07:27 PM   #211
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The ambient conditions were actually quite cool when we first left home. Perhaps in the '60s and '70s so I knew I had plenty of cooling. But in one measurement I saw that the temperature of the gas entering the condenser was only 10 degrees above ambient which means it had been fully cooled before it ever reached the condenser so no liquid ammonia could possibly be formed in the condenser. At that same time the temperature at the boiler was 120 degrees which is way too low knowing that the heating element just 2+ feet away was at 320 degrees. All of that heat was being absorbed by the ammonia dropping back into the boiler from the moisture separator piping and the cycle was not extending to the full fridge.

It totally does seem counterintuitive, but I promise what I did so far does work and it works well. The reason it works is that the ammonia gas that is produces is a fairly low volume - it just bubbles up from the bubble pump like a peculator makes coffee - same mechanics. Water boils at 100 C / 212 F at sea level. Under prtessure as it is in the cooling unit, the value of boiling point is higher. Ammonia boils at -35.5 C / -28.1 at seal level, again, higher under pressure of the hydrogen in the cooling unit. That tells us two things - that the ammonia will boil before the water will but given enough temperature the water will also boil. It also shows that the ammonia can cool down to some low temperatures given the pressure it is under. I have no idea what the pressure is of these cooling units but I will find out because it helps to determine what a good boiler outlet temperature is and what is bad (boiling water). As the ammonia boils it carries away heat from the water and that regulates the temperature of the boiler. This is basic physics and the sort of stuff that I dealt with while I was working in power plants. What I would like to do is to ensure that the maximum amount of vaporous ammonia reaches the condenser without condensing prematurely in the moisture separator as it is doing currently without that baffling restricting the flow.

In cooling the fins, I believe that humidity will actually help the fridge remove heat but at a trade-off. The more humid the air, the more thermal energy it can contain. So humid air has the potential to remove more heat from the condenser. Our bodies cool by evaporation so more humid air isn't good for us. But the trade-off is that humid air also has more thermal energy in it and that air inside the fridge gets cooled to the point that the moisture condenses out, which is a change of state for that moisture and therefore takes cooling away from the food. Its like pouring a frosty cold beer in the desert - it will stay cool for longer than in a humid climate because of all the moisture condensing on the glass - that robs heat away faster from your drink at the same temperature.

I would like to find a balance point for ammonia production, moisture removal and cooling. That will take research but I still suspect that even a little insulation around that moisture separator piping will improve performance. I am willing to burn up old core to find out.
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Old 07-10-2013, 10:21 PM   #212
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Just for fun - check this out. It is really not much different than how our fridges run, only ours run in a continuous cycle whereas these run for a few hours before needing a recharge. But same ammonia and water mix.
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Old 07-10-2013, 11:18 PM   #213
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See post 11 early on by Howie, I did pretty much the same thing on my 86 excella and all my problems went away. Have you built/installed a wall as per Dometics specs?? you should,
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Old 07-11-2013, 08:52 AM   #214
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I would need to see more pictures of what Howie did but no, I have not built a wall. The sides of my fridge are tight against the cabinet on one side and the wall on the other side is where the bar sits. With the fridge fully inserted into position the coils actually sit into a little hole cut in the inner skin layer. There is no room for much of a wall. But hey - fridge works great now for us.
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Old 07-11-2013, 12:05 PM   #215
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I'm truly comforted that you ability to make ice for your adult beverages is solved.
Travel safe.
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Old 07-28-2013, 10:16 PM   #216
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Originally Posted by perryg114 View Post
Any unit

Perry
In looking around the Amish site for fans, parts and such, I noticed that they now sell all new cooling units, with heavier tubing and some other changes from the standard rebuilt ones.

Not for every refer, but a lot of them, it seems.

Have you seen or heard anything about those, Buttercup? They are still a lot less than buying a new complete refer, at least up here.
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Old 07-31-2013, 02:13 PM   #217
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Quote:
Originally Posted by Aage View Post

In looking around the Amish site for fans, parts and such, I noticed that they now sell all new cooling units, with heavier tubing and some other changes from the standard rebuilt ones.

Not for every refer, but a lot of them, it seems.

Have you seen or heard anything about those, Buttercup? They are still a lot less than buying a new complete refer, at least up here.
I got an Amish rebuilt. I wanted to get a new unit but they didn't have any. So I took the rebuilt. About all I could say is that the heavier tubing probably doesn't have any great advantage over standard construction. I can't prove that of course. I could see changes in heat transfer by thicker tubing.

BTW, I have decided that I will keep the old unit and turn it into my play unit.
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Old 07-31-2013, 02:18 PM   #218
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Could the heaver tubing be a counter measure against the failure and fire they have had in the past? I believe it was the tubing that failed on those units.
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Old 07-31-2013, 03:19 PM   #219
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Could the heaver tubing be a counter measure against the failure and fire they have had in the past? I believe it was the tubing that failed on those units.
Good point, I don't know really where the problem is. It's the Hydrogen that is flammable. I'll research that. I would like to know myself.
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Old 07-31-2013, 04:02 PM   #220
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My recollection was it was a cracked tube that leaked. Always thought the sheet metal fix Dometic put out was a joke at best. Like as if h would not sneak around the corners.
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Old 08-23-2013, 11:50 PM   #221
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Just an update - to insulate the moisture separator components to preserve the heat content in the vaporous ammonia sections will not actually help as it will likely induce extra moisture to pass through the "rectifier" sections and that will condense in the freezer section and stop up the whole
works. That section of tubing MUST release some heat to condense out the water in the ammonia. To insulate that section of tubing would only cause new problems, not solve them.
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