My Hydroflame furnace and Atwood HW heater both have high temp cut off's. The furnace has several models of thermal cut off's, 130F, 170 F and 190 F elements are listed in the Hydroflame tech manual. The high limit switches are in the safety control circuit. And yes the energy used in both of these is a lot more than the fridge and in the case of the HW heater or furnace, it is a must.
On the fridge, if there is no DC running to the unit, it will not operate regardless if on propane or 120 electric. So a high temp switch could be put in the DC power circuit to the control board and it would shut down both the gas and the ele element. Problem most likely will be that the current draw on the DC power circuit will be to much for the normal high temp switch, so a relay would be needed as well. High temp switch runs the coil on the relay and the relay contact takes out the DC power.
OR better it be added in the control circuit that goes with the power on switch in the front of the unit. If the wiring diagram would be a full blown schematic I could read the circuit diagram and figure out the internals of the circuit board. Have had a level of TTL logic design from years ago, before everything went programmable.
The raw cost of these components is not much.
Now granted the high temp cut off will not solve the thermal expansion cracking issue nor is it probably a mandated item. But it is a good idea after the realization of what can happen. Like Chris said it could help prevent a leak problem from getting worse. Like Tim saw, if the coolant drains out the heating element and things starts glowing red hot.
I'll have to dig in my handbooks on the approx surface temp of red hot metal but it is safe to say it is in the combustion energy range of wood. As a point of reference, soft steel melts at 2,500F. We are no where near that hot, but when the metal is glowing red, it would not surprise me that it is over 1,000F. And as another point of reference, a dry pine board has an ignition point of ~ 500 F.
If the comments that Dometic has a high temp cutoff on their newer units is actual, then the parts are already available and they have figured out the easiest way to put it in he control circuit. A working diagram or a pic of a new unit would reveal this. I would have no problem paying for the parts to install this. $50 is not a big deal here for those that can do this themselves.
Tim or Chris, if either of you have even a broke unit that a good pic of the ele element well can be taken with all the insulation striped back and the fitting that cracks would be great. I know the actual failed unit Tim had is in the trash heap by now but even a non failed one will help.
Seeing the suspect area close up, knowing the surface temps the 354 watt surface element brings the metal up to are key info. With the new age of Finite Element Analysis, this fitting area can be modeled and the thermal expansion stresses predicted. And metallurgical analysis of a failed unit will reveal the exact cause of the failure. This is common practice in the industrial machine building world. We do both at work often to back into why stuff broke. I'm sure Dometic has already done this. Or at least assume they would.
Good discussion by all.
John
