I recently installed a gadget that will shut off the refrigerator if the boiler temp exceeds a threshold temperature. Our original refer "bled out" in less than two years and was replaced under warranty. The literature of the vendor, ARP, convinced me that spending $135 was worth it to prevent another failure. I am not a metallurgist, so I can not confirm the vendor's claims, but they seem reasonable to me. Specifically, that metal fatigue is cumulative. Overheat metal enough times and it will fail. Parking unlevel with the refer on will cause the boiler temp to rise. Do it enough times or leave it unlevel long enough and the tube holding the ammonia will crack open.
We park level for the night, but we are guilty of letting it go when parked for lunch or stopping by a friends house for just a short while. Yes, could shut off the refer, but the simple fact is, we forget. If your memory is better than ours, you can save your money and read no further.
[BTW, if your refer "bleds out" you do not need to replace the whole refer, just the working part of it. The part outside. The part that costs one-half of a new refer. The part that does not require removing a window to install it.]
The device vendor is ARP. The web site is http://www.arprv.com/ Since I had already installed two cooling fans OUTSIDE, I bought the plain Jane model. If you do not already have outside cooling fans and you camp in warm areas, such as the desert SW, you should consider getting the device with fans. On reflection, I should have tossed my existing fans and bought the full boat ARP device with fans and let the device cut the fans off and on as needed.
If you want to install the device inside, also order the additional cost longer wiring. I had enough wire on hand to do the job. The gadget will work fine installed outside in the refer service compartment, but I could not resist having another digital device inside. [As one of the more knowledgable contributors to things Lazy Daze said, You are more anal than I am]
Installation - The manual is written by an engineer. Unless you read engineer, you may be mystified. It is made even more nebulous as it covers all Dometic and Norcold refers at the same time. I got lucky and found one drawing that closely resembled the wiring we had. With a VOM, I was able to make a educated guess of how it must work. I then called the vendor and he confirmed my suspicions.
In the photo below, there is a thermal shut off device on the boiler housing at the right of the picture. This is the Dometic device that is supposed to shut the refer off if the temp exceeds whatever temp the device is set for. [Note, that it will not shut off if the temp approaches, but does not exceed the threshold multiple times]
I found that this wire comes from the control box, carries 12 volts and returns there. This is what needs to power the ARP device. All that needed to be done was to enlarge the loop placing the ARP device in the loop. So to the device inside, I ran two wires one to carry and one return 12 volts. I also ran a ground wire as I could not figure where I might find ground inside the cabinet above the stove. [This is a MB]
Installing the temp sensor required removing the housing shown in the picture above. Then parting the fiberglass so you can clip the sensor to the boiler tube. This requires small hands, as the LD compartment is not really tall enough to make it easy. Be sure to put on thin gloves or spend the rest of the day picking FG out of your hands.
How to run the wires. It ain't fun. Mike Sylvester installed our solar panels and ran wiring from the battery compartment, below the refer access compartment on an MB and up the refer cooling tower to the roof and then through the front wall of the cabinet above the stove and then down to the charger. I used the same path. Mike had left a pull cord anchored to the refer vent on the roof. That helped. [You probably don't already have this pathway, so just drill a small exploratory hole from inside the cabinet, at the top, forward into the cooling tower]
I elected to hide the device inside the bin as it was slightly larger than the space about the refrigerator which would have been ideal location. Here it is showing the boiler temp. Ours high reading is 190.