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 > Absorption fridge tests and new safety device

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Gdetrailer

PA

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Posted: 12/11/13 04:01pm Link  |  Quote  |  Print  |  Notify Moderator

I have been stating for YEARS that operating an absorption fridge off level of ANY AMOUNT affects the fridge in a bad way...

Well, I noticed on a different RV forum that there has been some testing of this theory.. AND it PROVES my assumption..

It detects unsafe temps of the boiler and can shut down the fridge BEFORE the Norcold safety device detects overheating.

I would highly recommend folks to READ the link below..

FRIDGE PROTECTION DEVICE

For those too lazy to look at the link here is some of the text from the opening post..

"I'll apologize in advance if this sounds like a sales pitch: it is not. It's a report of what I learned while participating in a field test of a new device designed to protect RV absorption refrigerators. In doing so, I became a lot smarter about how these fridges work, and came to respect the engineering that went into designing the ARP device. So onto the report...

RV fridges made in the last 20 years claim to be fairly tolerant of being off-level and generally are spec'ed to allow up to 3 degrees side-to-side and 6 degrees front to back. That's from the perspective of the fridge, which is normally sideways in the RV, so it's 3 degrees tilt fore & aft in the RV.

Recently, though, I've been helping Paul Unmac test his invention, a patented device called the ARP that will control the heater (boiler) in an RV absorption fridge in a much narrower range than the factory control board. Paul believes this will extend the life of an RV fridge as well as preventing fires in failed cooling units. One of the test beds is a skeleton Dometic 6 cubic foot fridge set in a portable frame that can be carried around (for demos) and tilted in any direction at will. With an ARP installed and its optional data collection package connected, we can watch how the boiler reacts when the cooling unit is tilted.

The results amazed me! Merely tipping the fridge a few degrees to one side (by sliding a board under one edge), the boiler temperature immediately soared! And I do mean soared - it climbed over 100 degrees F, in less than two minutes and showed no signs at all of stopping. We quickly re-leveled the cooling unit to avoid damage - Paul didn't want to risk the unit he is using for demonstrations at RV shows this fall and winter - and the temperature began to fall again nearly as quickly. I'm sorry I failed to get a picture of the display graph as the temperature climbed, but I was literally too amazed to click the shutter!

Why does the temperature climb? Basically because the ammonia refrigerent solution stops condensing back to a liquid and flowing back into the boiler at the end of the cycle. Without liquid in the boiler, the temperature shoots up quickly, guaranteeing that the cycle won't restart on its own becasue it is now too hot to ever cool sufficiently. It's a vicious cycle that quickly gets out of control after even a brief hiccup.

RV gurus have been telling folks that their fridge is OK if they can walk around comfortably, but now I'm not so sure. According to Paul's research, high boiler temperatures cause the internal rust inhibitor (sodium chromate) to crystallize and lose it rust preventive qualities. Loss of the sodium chromate increases allows the extremely corrosive ammonia to attack the steel tubing and eventually cause a leak. And a leak is both a failed cooling unit and a fire risk. The sodium chromate crystals (they yellow stuff you see in a failed cooling unit) is also the main ingredient in a clog that can block flow through the condensor and evaporator tubing. Without laboratory testing I can't guess how much sodium chromate is lost, how quickly, and how much temperature rise is needed to cause it, but I think there is sufficient cause for concern.

Another thing I have learned by having the ARP data collection package installed on my own coach is that the boiler temperature can swing widely while driving. Mine actually was getting about 25 degrees (F.) cooler while underway at interstate speeds, and that is enough to cause the temperature in the fridge to rise (which I have observed). I can also see the boiler temperature move quickly when I pull into a rest area, slow down in traffic, or stop at the campground office to check in. The changes are immediate and dramatic. Paul says that climbing a highway grade also causes wide swings, sometimes hundreds of degrees. I surmise that wind is blowing down from the roof vent while driving ay highway speeds and that cools the whole process off. I have since added insulation around my boiler area but haven't been out on the road to see if it helps stabilize the temperature.

Paul has also measured temperatures on fridges installed in slide-outs and found then running substantially hotter than non-slide fridges. Slide-mounted fridges have the upper vent in the side and do not provide as much air flow over the coils as roof-mounted vents. He recommends adding a good sized fan at the bottom of those fridges to improve cooling unit performance as well as extending its life.

As part of the testing I arranged for about 20 others RVers to install an ARP and give feedback. All are working fine and there have been no complaints of any kind, either problems with the ARP or impact on normal fridge operation. Since then Paul has been selling the ARP at RV shows and online via his website. I don't know sales numbers, but it's into the hundreds.

There is more information on the ARP controller and absorption fridge characteristics on Paul's web site, ARPrvSafe

I have no financial interest in this product but I did receive a free controller and data collection package in exchange for my help in testing it. "


SWD

Land of Living Skies

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Posted: 12/11/13 04:18pm Link  |  Quote  |  Print  |  Notify Moderator

Interesting.......but what amazes me is that if the fridge should sit level, why in the heck is the rv builders cabinetry skills so out of level. I can get my trailer level but have noticed, not just on mine, that the surrounding cabinets are not. Poor quality control all around.

pianotuna

Regina, SK, Canada

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Posted: 12/11/13 04:41pm Link  |  Quote  |  Print  |  Notify Moderator

Hi SWD,

That is why I leveled my fridge--and then installed the bubble levels. But I agree, quality control and RV rarely belong in the same sentence.

I'm interested in acquiring one of the units. But I wonder if a simple "snap disk" thermostat would not work?


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Gdetrailer

PA

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Joined: 01/05/2007

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Posted: 12/11/13 05:09pm Link  |  Quote  |  Print  |  Notify Moderator

SWD wrote:

Interesting.......but what amazes me is that if the fridge should sit level, why in the heck is the rv builders cabinetry skills so out of level. I can get my trailer level but have noticed, not just on mine, that the surrounding cabinets are not. Poor quality control all around.


RV builders simply use the manufacturers "tolerances" given, it isn't the "builders" job to make it "dead on" plumb or level, it is the END USER that must ensure the fridge operates as efficient as possible.

The data that they have collected clearly points the fact as I have argued so much about on this forum that level MEANS ABSOLUTELY 100% IN THE BUBBLE.

The fridge manufacturers have a lot to gain (and hide) by allowing lax tolerances to being off level.

By BLINDLY following the published 3degree/6degree tolerances from the manufacturer the end user is SHORTENING the actual life of their CU. And from the gathered data I would have to say that even slightly out of level DOES affect the cooling unit by raising the boiler temps well above normal operation.

Pretty simple, the entire CU relies on gravity and is most efficient when completely level.

Why?

Simply put, a slight change in the orientation of the tubing causes more resistance to fluid movement inside the tubing. It basically increases FRICTION inside the tubing and FRICTION slows down the movement inside the tubing.

"Dead On" level represents the LEAST AMOUNT of friction encountered inside the tubing... Therefore IS the "best way" to operate your fridge.

Kudos to those folks on the other forum, the data they are collecting just might help folks SEE the real facts in how the fridge works...

Gdetrailer

PA

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Joined: 01/05/2007

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Posted: 12/11/13 05:13pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hi SWD,

That is why I leveled my fridge--and then installed the bubble levels. But I agree, quality control and RV rarely belong in the same sentence.

I'm interested in acquiring one of the units. But I wonder if a simple "snap disk" thermostat would not work?


Snap disks placed in the correct place might in a pinch "work" but it would be trial and error not to mention snap discs come in a variety of on/off temps and may have too wide or even narrow hysteresis.

I suspect that their ARP is a bit more involved than a simple snap disc especially when it can be teamed up with some sort of optional data collection module..

SWD

Land of Living Skies

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Posted: 12/11/13 05:25pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hi SWD,

That is why I leveled my fridge--and then installed the bubble levels. But I agree, quality control and RV rarely belong in the same sentence.

I'm interested in acquiring one of the units. But I wonder if a simple "snap disk" thermostat would not work?


Did the same thing....leveled the fridge then put on the bubbles.

Old-Biscuit

Verde Valley

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Joined: 06/20/2009

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Posted: 12/11/13 06:21pm Link  |  Quote  |  Print  |  Notify Moderator

Post from 12/8/2013 discussing off level operation (one on numerous posts).......LINK

Notable post by Chris Bryant on 1st page.


Is it time for your medication or mine?


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popeyemth

owensboro ky

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Posted: 12/11/13 06:25pm Link  |  Quote  |  Print  |  Notify Moderator

SWD wrote:

pianotuna wrote:

Hi SWD,

That is why I leveled my fridge--and then installed the bubble levels. But I agree, quality control and RV rarely belong in the same sentence.

I'm interested in acquiring one of the units. But I wonder if a simple "snap disk" thermostat would not work?


Did the same thing....leveled the fridge then put on the bubbles.


How did you level the fridge-from the inside or the framework or...
PM me if you wish. I intend to level mine.
Thanks,Mike


"wine is a constant proof that God loves us, and loves to see us happy" ben franklin

Francesca Knowles

Port Hadlock, Washington

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Joined: 02/23/2011

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Posted: 12/11/13 06:48pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:



Well, I noticed on a different RV forum that there has been some testing of this theory.. AND it PROVES my assumption..


"Testing of this theory"???? One guy does his own backyard testing, identifies a "problem", invents something to solve that "problem", and puts up a website to sell it.

I wouldn't call that "tested proof" of anything except that there'll always be a market for new gizmos. We'll see how it sells...


" Not every mind that wanders is lost. " With apologies to J.R.R. Tolkien

pianotuna

Regina, SK, Canada

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Posted: 12/11/13 07:29pm Link  |  Quote  |  Print  |  Notify Moderator

Hi,

I used two small carpenter's levels in the freezer set at 90 degrees from each other.

I'm pretty certain that I'll get one of these devices in the near future. If it is good enough for Chris Bryant, it is good enough for me.

popeyemth wrote:

How did you level the fridge-from the inside or the framework or...
PM me if you wish. I intend to level mine.
Thanks,Mike


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