My twenty year old Dometic RM1282 continues to work flawlessly on both gas and AC power. In spite of this, reports of RV refrigerator fires in recent years have become a concern. These fires occur because of damage to the refrigerator’s boiler tube due to overheating. Commercial devices are available that prevent this overheating but I’d never got around to pulling the trigger to order one. A few months back, a fellow iRV2’er posted a description of an inexpensive homemade device that could prevent the overheating problem. Here is a description of my installation of this device.
The device itself is described as a High Temperature Thermostat and it costs less than $20. This circuit board, with digital temperature readout, comes with a temperature probe and has an onboard relay that operates as an on/off switch for an external device (your refrigerator). This thermostat operates off 12 vdc and has a range of 30–999° Celsius. Operational parameters are easy to set.
After receiving the device, I familiarized myself with its setup using a cup of hot water and a cup of ice water. With my (cheap/free) Harbor Freight meter, I watched the relay switch open and closed as the temperature probe was moved from cup to cup. Convinced that I understood how everything worked, I mounted the thermostat in a small plastic box (recycled from a box of screws from Lowes).
Before the actual installation, I modified the supplied temperature probe for better results. The probe was made for a screw-in application so I removed the threaded part, with a cheap Harbor Freight file set, to end up with a small cylindrical probe. This process took about 5-10 minutes and provided exactly what I was looking for. I then fabricated a clip, from a hose clamp, to hold the probe against the refrigerator’s boiler tube.
For installation, I followed the same instructions found in videos for similar commercially made protection devices. Simply gain access to the boiler tube and mount the probe as high as possible. Best results are obtained if the probe is mounted above the indentations in the tube.
My refrigerator has a control board that operates on 12 vdc. If this 12 volts is removed, the refrigerator turns off. Return the 12 volts and the refrigerator turns back on. Actual testing proved that this happens if the refrigerator is in AC mode or Gas mode. If the supply line for this 12 volts is connected to the relay on this thermostat board, it will control the power to the refrigerator, turning it off and on.
After everything is in place, it was time to set the thermostat to control the refrigerator. To determine the normal operating temperature of the boiler tube, the thermostat was set for 300° Celsius. With the refrigerator operating on gas, the readout on the thermostat was observed for several hours. The next day, after a total cool down period, I tested again with the refrigerator operating on AC. In either case, the temperature never got above 182° Celsius. With this figure in mind, I reset the thermostat to cut off power if the temperature reached 185° Celsius and turn back on at 182° Celsius. I have monitored this on a couple outings and it seems that 182°C is my maximum operating temperature.
If you install this board, you must perform your own temperature test because every installation is going to produce different results. Contributing factors for this are the age of the refrigerator, its usage and the mounting position of the temperature probe. Another point I should make is that your off/on temperature settings will be maintained by the circuit board even if it is disconnected from its power source (such as turning off your salesman switch).
Because the thermostat board was so cheap, I bought a spare just to have an extra. Should the board fail, you can easily take it out of line by removing the wires from the relay and twist the ends together. This will return your refrigerator wiring back to its original state.
Does this inexpensive device provide the same safety as the commercial units? I don’t know. Am I happy with my investment, installation and feel more secure? I certainly do.
Feel free to PM me if you have questions but I prefer to reply via email. I usually read this forum with an Android tablet app which makes typing a reply slow.
Special thanks to iRV2 member nehog for his mention of this device and answering some of my questions.
Device name: Mini High Temperature Thermostat
Model number: 34687-MP
Company: Marlin P. Jones & Assoc., inc
Web address: www.mpja.com
Price with shipping: < $20.00