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Old 04-19-2007, 01:44 PM   #15
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Originally Posted by Fyrzowt
If you do a Google there is info out there. The link below has some info with photos of RVs after fires. Significant if it is your RV.
Dave

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Looks like I should put the batteries back in the smoke detector. Also looks like Dometic is ahead.
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Old 04-24-2007, 06:17 AM   #16
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Quote:
Originally Posted by Fyrzowt
If you do a Google there is info out there. The link below has some info with photos of RVs after fires. Significant if it is your RV.
Dave

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Got this pic from the link fyrzowt posted. Typical late model dometic, if you look at the horizontal tank, you will see the service port on the end. The stem in that port is drilled and filled with lead. In the event of a fire from the burner area below it, for example, the lead melts and releases the pressure from the unit. But the problem is that when it does this, the hydrogen catches fire and you got a instant blow torch that burns everything it touches. If only the manufactures would use helium instead of hydrogen, alot of fires could be detained. To my knowledge I'm the only rebuilder in the states that uses helium. It's twice as expensive as hydrogen but it's worth the safety.
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Old 04-24-2007, 06:32 AM   #17
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Sounds to me like we all have the Hindenburg in our RVs!

Same story, just a bit different setting...shoulda, coulda, woulda....used Helium instead of Hydrogen.
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Old 04-24-2007, 07:12 AM   #18
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RV Cool has it right-on! But as is standard operating procedure in the business world of today, saving a couple of bucks on each unit that they produce, KNOWING OF THE INCINERATION RISK, is common practice, and you have to take your chances! Sometimes it works and sometimes they get caught with their pants down!!

I could detail dozens of areas that I've seen in RVs where a buck or two spent using a better part in the building process would have saved the company hundreds of dollars on the back end paying for a warranty repair. They just don't get it!

That said, the probability of your electric element igniting the escaping hydrogen is far smaller than the open LP flame starting the fire. On EVERY cooling unit I have replaced, these refers WERE OPERATING ON ELECTRIC when the failure happened and with few exceptions, the tube rupture occurred in the boiler section. This is the area in question on the Dometic recall. NOT ONE HAD A FIRE !!! Just a big yellow mess from the leaking sodium chromate.

Yes, the chances are small that you will have a fire, even operating on LP. But do you really want to take that chance! If my unit was included in the recall (it isn't), I would pre-cool it for a day on 120VAC, keep frozen blue ice or water in the refer section, and use the LP ONLY when I was there to watch over it, if at all, considering that there was no 120VAC available. The other option is a small generator to run the fridge on electric, so you don't have to use the LP at all until it's fixed. A 1000 watt gen will do this with no problem, as the heating element is less that 400 watts.

Remember, after spending those hundreds of hours in restoration or those big bucks for a new(er) unit, you don't want it going away any time soon from something that you now know about and have control over!
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Old 04-24-2007, 07:26 AM   #19
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Lew, it sounds to me like the main goal here is fire suppression, not prevention in the event of a tube crack caused by the higher wattage heating element.

My question is about the cost of helium to be placed into these units. It sounds to me that at some point, there is a higer than average chance these units involoved in the recall will fail at some point. If that is the case, maybe it would be a great idea to do the right thing when it comes time to rebuild the unit? Is it cost effective to drain the hydrogen somehow, without blowing yourself up and installing helium before it's an issue?

What would an average person expect to pay for a fridge, pre-failure to have the hydrogen removed and replaced with helium?
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Old 04-24-2007, 04:11 PM   #20
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Twink,

Tough question to answer, as I don't get involved in the actual re-build process. PM 'RV_cool' . He actually does this process and can give you the specifics of hydrogen vs. helium pricing.
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Old 04-24-2007, 07:49 PM   #21
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Basic question then,, after all of the above is read and digested,,, is this fix a real fix or just a precaution for Dometic??? How safe are the models that are affected??? am quite concerned,,, thanks,, donna
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Old 04-24-2007, 09:09 PM   #22
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I won't really know until I get my first recall kit. Itd's impossible to say at this point, but I'll post as soon as the first one arrives.

Hopefully, they will get here soon, as I'm getting a lot of calls on this and have NO PARTS YET
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Old 04-25-2007, 09:55 AM   #23
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The "Kit" was installed in my trailer last Saturday. It is a joke. All the "Kit" consists of is a Limit switch wired in series with the 12 volt supply line for the refridgerator control board and some sheet metal pieces that were not even used in my case. There is no lower wattage electrical element. Nothing to reduce any eventual metal failure that would release the Hydrogen gas.

Now lets just think about this for a second. If you have a crack failure in the refridgerator system that releases Hydrogen gas that has then been ignited to produce enough heat to trip the high limit switch do you real think cutting off the power to the refrigerator is going to do anything. Oh yes and by the way the only way you would know the system has failed would be the lights on the monitor of the refridgerator would go out or you would smell the smoke

There are 3 ways to put out a fire. Lower the temperature, cut off the fuel, cut off the oxygen. This system does none of them. I would assume all Dometic has done is ackowledge a problem and provide a blantanly inadequate solution. Not sure I would want to be thier insurance carrier.

Is there any indication that the newer units are any better or have they just installed the limit switch in them at the factory?
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Old 04-25-2007, 11:42 AM   #24
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Howie,, great question,, i too am awaiting the same answer,,, thank you for posting,, donna
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Old 04-25-2007, 07:58 PM   #25
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As I have stated in previous posts, I have not seen the kits yet. That said, when they were initially described to me by Dometic Tech, the extra sheet metal was to be used as another location for the heating element to be positioned. There also was to be a 'shield' that would re-direct any potential leak of hydrogen coolant away from the element, thus decreasing the possibility of ignition and fire.

From what I was told...ALL OF THE PARTS SHOULD BE USED IN ALL INSTALLATIONS! HowiE, I would go back to your installer and ask them point blank why they didn't install the extra sheet metal, and if they insist that it should not be used, ask to see the Dometic instructions that directed them to do so.
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Old 04-25-2007, 09:36 PM   #26
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I saw but did not study the 4 or 5 pieces of flat sheet metal in detail. The installer said they were optional depending on the model. The larger piece was to be installed in a place that my refg. already had an equal sized piece of sheet metal. He used mine because it had the drain hose going through it. The only metal he did use was the holder for the limit switch.

We did discuss what a joke the kit was. When he had originaly heard about the problem he had assumed the complete cooling system would have to be replaced since the kit does nothing to reduce the mechanic failure that would cause a leak and less to supress a fire. All it does is shut of the 12 volt supply if the temperature behind the refg. gets too high. If that temperature rise is the result of a fire you have already lost the game.

Oh yes the only indication you get, other than a fire, is the fact that the control panel light will go out.

Yes I would be interested in seeing the instruction.

If Hydrogen gas escaped into the heating area of the refg. no sheet metal would have any effect.

As one of our posters notes at the end of all his posts.

"The Ark was built by amatures the Titanic was built by profesionals".

This "Kit" has all the ear marks of another professional job. Don't let your insurance laps.
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Old 04-26-2007, 01:25 AM   #27
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The ark may have been built by an amateur, but don't forget - he was using God's blueprints.
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Old 04-26-2007, 05:48 AM   #28
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I have proven myself wrong

Quote:
Originally Posted by RV_cool
[IMG]... To my knowledge I'm the only rebuilder in the states that uses helium. It's twice as expensive as hydrogen but it's worth the safety.
From what I know about RV refigerators, I read that comment thinking that hydrogen was used because it had better physical properties than helium for use in gas absorption applications and NOT because it was cheaper. Part of my mindset came from having never thought about using helium until RV_cool mentioned it. It appears that helium, in addition to being safer, is actually beter:

Quote:
Originally Posted by Numerical investigation of a diffusion absorption refrigeration cycle

Abstract

A thermodynamic model was developed for an ammonia–water diffusion absorption refrigeration (DAR) cycle with hydrogen or helium as the auxiliary inert gas, manufactured by Electrolux Sweden (currently known as Dometic). The performance of the system was examined parametrically by computer simulation. Mass and energy conservation equations were developed for each component of the cycle and solved numerically. The model was validated by comparison with previously published experimental data for DAR systems. Investigation of cycle performance under different conditions indicated that the best performance was obtained for a concentration range of the rich solution of 0.2–0.3 ammonia mass fraction and that the recommended concentration of the weak solution was 0.1. It was also found that as the degree of rectification decreased, the performance of the DAR cycle decreased. Finally, the study showed that helium was superior to hydrogen as the inert gas: the coefficient of performance of a DAR unit working with helium was higher by up to 40% than a cycle working with hydrogen.
Live & learn.

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