John wrote:
We keep it up and we may actually understand the real problem. We are in lack of a good picture of the boiler tube area where the crack is located.
Hi John, while reviewing the thread there's little doubt in my mind that the culprit is two fold. I do believe between Dometic's recall paper, only fridges with the underrated element (354w???),Tim's post about the common factors to the failures was the underrated heating element and that it failed at the first weld above the elbow, plus Chris' post on the effect of stress from heating the weld.
A big question in my mind "Why such a low failure rate?"
There's also no doubt in my mind that a lot of failures happened but for reasons unknown (not reported)are not included in the statistics. Yet theres much reason to believe the failure rate is still low.
Now here it gets kind of iffy, Chris most likely could explain this better.
Those who have welding experience will understand there is a quality of weld depending on the penetration (mix of new metal to the pieces being welded)when heated the stress characteristics of this welded joint are quite different to the surrounding metals. It's easy to believe that a lower number units might have a much deeper weld penetration than the rest (new or novice welder)and when overworked by an excessive expansion and contraction, the weld will break from from one of the metals that were joined leaving a very weak structure.
No matter which parts list you look at the parameters for a 325 watt element is 44 ohms +/- 10% if your fridge has that it's not on the recall list. There is a reason for this, an absorption refrigerator must have the correct heat to operate. The low end tolerance is 39.6 ohms, so it is safe to assume this would generate the hottest allowable temperature and the expansion and contraction factor does not overwork the weld.
Now what I know from my refrigerator. It was put in service May 2000 in a RV rental unit five years before I bought it. The element I removed, was stamped 325w at 120v, however the element itself measured only 38.5 ohms. This is certainly much below tolerance and capable of heating and working the weld beyond the normal expansion caused by a true 325w element. Unless it's the quality of the weld that has prevented failure I have no idea. Also this may be true of the majority of units out there
Did Dometic know these elements were out of the +/-10% tolerance, of course they did, they printed the parts list to read 115v 325w so now it's back in tolerance. ( I have the parts list and the element, they can explain the rest)
The Dometic modification to the best of my knowledge, from what is posted on this thread, consists of a fix so that the unit does not catch fire when the cooling unit fails while operation on LP gas.
So What to do. I don't know about anyone else but here's my reaction.
1 Replace the heating element with a new one of correct specifications (preventative, why push one's luck)
2 When the Dometic fix is ready, have that done (Safety, it's free why take a chance)
3 When we have enough information I will install the thermal cutoff. (more safety, it's easy to do so why not)
Because of the thread I believe we have a better understanding of the problem and remedial actions we might take. At least now when we go out for a run I'll feel a lot better about it all than when the thread first started.
Cheers Willis
