I have received and bench tested the thermostat I purchased for this mod so that I know how it works. Haven't played with the bonus app yet, but that should be fun.
https://www.amazon.com/Temperature-Controller-99%C2%B0C-999%C2%B0C-One-Channel-Thermocouple/dp/B09TT7VWCK
Pretty straightforward once I figured things out. This thermostat operates a relay. I will ultimately run the 12v power going to the refrigerator control board from the "on/off" button control inside the RV through the relay. This should cover either AC or propane operation (they both require the 12v supply to the refrigerator control board). That same 12v line will supply power to this thermostat device, so it will only be on when the refrigerator is on (no power draw while in storage).
I can set a high "turn off" temperature and will likely have that at 200*C (392*F) (assuming that "normal/level" steady boiler temperature is ~180*C (356*F)...I will test this once it is installed). My understanding is the primary goal of this, or similar, device is to simply keep the internal water in the cooling unit from boiling (220-225*C...428*F-437*F...and higher). (side note: If you are wondering WHY the water boiling point is so high inside the cooling unit it is because the system is under a lot of pressure during operation.) If the boiler hits 200*C (perhaps by being out of level), the 12v power to the refrigerator will be killed (which will be sort of equivalent to turning the refrigerator off at the main "on/off" button) until the temperature drops down to some set point and then it will turn back on automatically (nice...this is what we want). I'm not sure what temp I should set this drop down temperature to. Any thoughts?
If it turns off at 200*C, do I want it turning back on once it drops down to 180*C? 150*C? 70*C? Unless someone explains otherwise, I think I'll have it turn back on once the boiler cools down to 170*C (338*F). That would be a 30*C cooling off period (from 200*C) which I'm guessing would take 10-20 minutes (??? I'll try to do a test to find out once I install it). Then the refrigerator would turn on again and try again. If the conditions were still present that was causing it to start overheating in the first place (ie. being too far out of level), then the boiler temperature would slowly rise up to 200*C and then bounce back and forth between 200*C and 170*C. Any harm in this??
Or would it be better to have the boiler temperature bounce between 200*C and 180*C such that refrigerator interior cooling can hopefully still be taking place and the interior of the refrigerator can get to its desired temps and then the regular refrigerator controls would shut down the refrigerator until it needs to cycle on again naturally?
I'm guessing it probably doesn't matter too much if the "turn back on" temperature is 180*C, 170*C, 150*C, etc. The main purpose/function is to simply limit the overheating such that it never gets above 220*C (428*F). I'm still pretty stunned to know that Norcold and Dometic find it okay to let the boiler temp get all the way up to 750-800*F before their kill fuse blows (at which time, correct me if I am wrong, the fuse will need to be physically replaced before your refrigerator will work again). With my ~$25 mod it will cut the power if it gets just 36*F above normal operating temps and then turn itself back on once the boiler temp gets back down to normal.
I have some family in town for Christmas so the install will likely have to wait until early January.
-Chris
