Fridge: How Level is "enough"?

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Gary RV_Wizard

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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 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 1.5" 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!

We've been telling folks that their fridge is OK if they can walk around comfortable, 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.  Without extensive laboratory testing I can't say how much 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 causes 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.

There is more information on the ARP controller and absorption fridge characteristics on Paul's web site, https://sites.google.com/site/arprvsafer/

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.
 

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carson

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Interesting, Gary.  Now is the time for an entrepreneur to come along and devise a hydraulic leveling system:  4 ram type cylinders and a pumping system controlled by an electronic controller. Piece of cake except for the wallet.  Patent not applied for yet. ::) 8) ;)

 

kjansen

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Gary,
Could you post a picture of the insulation you added to you unit.  My 5er came with 2 computer type fans that are on a thermstat, but I have only heard them kick in 1 time.  Couldn't figure out what was running so I pulled the vents and found them.
 

Jeff

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After owning Dometics in 5 motorhomes it surprised me how hot the Nocold got if we were slightly off level and while traveling which was one of several reasonsxwe repkaced it with our Samsung. I don't know if it brand or unit specific but your monitoring system will probably open a lot of eyes.


Has your friend come up with a price target yet?
 

Kim (skyking4ar2) Bertram

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I think the fact that you and Paul now have some empirical evidence about the effects of leveling an absorption fridge is very important.

If your conclusions hold up in further testing, it would be something many consumers should consider monitoring.

The loss of a motorhome (or someone's life) over something so easily monitored and controlled as leveling the fridge should become a thing of the past. Kudos for your work and for sharing your results!

 

Mavarick

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Wow, very interesting. Wonder if this would be news to say a Dometic engineer or if this is just calculated into the lifespan. With all the trouble they have had in the past with these fridges I can?t image they wouldn?t have already figured most of this out right? With most items tested to failure I would guess the prevention methods were not cost effective until the safety factor is brought into play. Glad you shared all this testing though, I for one will pay a little closer attention to when I use the fridge and how level it is.
 

Gary RV_Wizard

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Both Dometic and Norcold let their fridges pretty much run wild. The Norcold 1200 safety shut-off doesn't activate until something like 800 F (normal run temp is around 360 F.).  They just tell you not to run off-level for very long and say it's your fault if you do.

Of course the fridge doesn't self-destruct immediately if it runs hot, but why let it get ultra hot at all?  Once the boiler is hot enough to boil the ammonia solution, it can't get any more efficient at cooling, so there is no need to let it do so.  And it's pretty simple to hold the temperature down by cycling the heater off/on as needed, and it wouldn't cost much to include that on the controller circuit board. .  Well, Paul now holds a patent on the device that does that, so maybe they lost out!
 

rebelsun

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I hadn't given it much thought until I read this thread.
But on our return trip from Ma. to Fl. in Sept. of this year, we were at a standstill on I-95 in N.C. for at least 1/2 hr., on a fairly steep hill, because of a major crash, involving a TT unit, and a passenger car.  The fire dept. had to cut the car apart with the jaws, to get the occupants out, and a medical chopper landed on the interstate to transport a patient to the hospital.
I guess we were lucky to not have the refrig. either stop working, or ignite the MH on fire, which in that traffic, would have caused a domino effect, with the other vehicles around us, and the FD wouldn't have been able to get to the fire, because of the previous crash, and the medical helicopter on the highway.

YIKES!

I'm seriously considering replacing the refrigerator with a standard, electric only, house type model, when the time comes.  I know the disadvantage, of that decision, such as not being able to run it on propane while traveling, but safety is my primary concern.  I wonder how high the refrigerator temp. went during that delay, as well as the bumper to bumper crawl up onto the GWB (George Washington Bridge), and back down on the NJ side, and all the other rush hr. traffic crawls we encountered around Boston, DC, southern Ct./NYC/NJ metro areas?????
 

Ernie n Tara

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Gary,

Intuitively it would seem that gas heat would be a greater problem than using electric. Is that the case or did you gather any comparative data? I know that I almost never run the fridge on  gas since I need the generator for AC in any csse.

Also, data on specific conditions would be useful. A one and a half inch block under one side of the fridge would be about six degrees on an average unit for example. That compares to about 18 inches front to back on a 30 ft Mh. That information combined with a curve on the rate of temperature change could make a bunch of laywers rich :-\ :-\

Regards,

Ernie

PS How old was the test refrigerator? It would seem easy to redesign the boiler (actually the cooling coil) to eliminate the problem.

Note: A 6% grade is about 21 degrees!
 

Gary RV_Wizard

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Has your friend come up with a price target yet?


The talk has been of a $120 MSRP when sold through a dealer, but he has been selling to test-bed users for $70.  He just sold some at the Good Sam Rally in Atlanta - I'll ask him what he charged there.

Paul says he is maintaining the $70 "introductory price" for now. The data collection USB cable & associated software is $40 extra, if desired. It's not needed to install or get the advantages of the ARP, but it's interesting to see what the fridge is really doing. The software is compatible with a Windows PC only.
 

Gary RV_Wizard

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PS How old was the test refrigerator? It would seem easy to redesign the boiler (actually the cooling coil) to eliminate the problem.

Indeed, one has to ask why neither Dometic nor Norcold have done anything to improve the design of RV fridges in all these many years. One would think that Norcold especially would be anxious to develop something they could call "new and improved", but they keep on selling the "same old fridge". Atwood, a newcomer to RV fridges, has at least made an attempt with the safer helium+ammonia RV fridge (the others use hydrogen+ammonia), but their product hasn't caught on with RV manufacturers yet.

I don't see how it's "easy to redesign", though. Ammonia is inherently corrosive, and the high temperatures and pressures involved pretty much dictate a steel container. And neither of those is a problem if the fridge is level and not moved around all the time - they last for 25+ years when installed in off-grid houses. Heck, Servel absorption fridges haven't been made since 1956 and some are still running in remote cabins!
 

Ernie n Tara

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I'm thinking that the heating problem is likely due to restricted circulation, or possibly bad burner design. Circulation restriction would probably be due to condensate getting trapped in the condenser when the tubing gets off level and the fluid has to try to run up hill.  An increase in the slope of the tubing should help avoid that problem although it would require more tubing $$$. I do recognize there is a balance required here to ensure flow under all operating conditions, but I doubt that is an insurmountable problem.

The boiler is even simpler to solve if it should be the probkem, unlikely in my opinion.

Ernie
 

weewun

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I have installed the ARP Protection device on my NorCold 1210 and my BIL's Dometic 1292 (not sure the # is correct) as part of Paul's Beta Testing.

For the dollars involved it is the cheapest insurance you can buy.  It, in no way, alters the manufacturer's design and build, thus should have no effect on Warranty  claims or manufacturer' liability.

Installing the ARP and collecting Data for Paul taught me a lot about the Frig.  I was pleasantly surprised about how powerful NorCold's internal Diagnostics are.

I was not able to track the temperature data on my way from NC to Naples, FL but the ARP did trip once during the trip indicating an overheat condition, I was very please that it did which proved to me that it works.

Paul's current Controller is head-and-shoulders above the one I have installed and is much more User-Friendly than the original, I may swap mine out.

I know this sounds like an advertisement for ARP but it has saved me the time and expense of installing a Res Frig as the people beside me last year lost their 2006 Tradition to a NorCold Fire and my DW was not comfortable with the NorCold, she is feeling better now.

I should add that if the ARP controller should fail it will not affect the normal operation of the Frig.
 

Phil Hyde

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Sounds like a great way to monitor a running fridge and keep it running reliably.  However, the evidence you collected suggests that simply turning off the fridge while moving is a good idea.
 

Phil Hyde

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vmax1 said:
Now I really want a residential fridge in my RV

My main concern with that, aside from the installation, is that a residential fridge probably isn't designed to be moved around constantly.
 

Jeff

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Phil Hyde said:
My main concern with that, aside from the installation, is that a residential fridge probably isn't designed to be moved around constantly.




Phil


I have not heard of any issues with the motion of an RV on a resodential model and several OEMs have been installing them for years. Air conditioners basically use tge same tyoe compresser system


And it certainly is obvious that gas absorbation shoukdn't be moved!
 

Jeff

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Gary RV Roamer said:
Indeed, one has to ask why neither Dometic nor Norcold have done anything to improve the design of RV fridges in all these many years. One would think that Norcold especially would be anxious to develop something they could call "new and improved", but they keep on selling the "same old fridge". Atwood, a newcomer to RV fridges, has at least made an attempt with the safer helium+ammonia RV fridge (the others use hydrogen+ammonia), but their product hasn't caught on with RV manufacturers yet.

I don't see how it's "easy to redesign", though. Ammonia is inherently corrosive, and the high temperatures and pressures involved pretty much dictate a steel container. And neither of those is a problem if the fridge is level and not moved around all the time - they last for 25+ years when installed in off-grid houses. Heck, Servel absorption fridges haven't been made since 1956 and some are still running in remote cabins!


For seventy bucks I'll bet Norcold or Dometic should be negotiating with Paul for rights to use his patent right now!
 
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