If you don't have a manual for the refrigerator
, just Google the Make and Model number followed by "Manual", they are all over the internet and you can print one out for free. If you can't find a manual, post the info here and someone will find a link for you.
Did you try the refrigerator on all 3 sources?
Sniff around for any ammonia like smell, if you can smell ammonia it's a terminal case and will require major repairs or replacement.
FYI: The Boiler Cover is the tall square or curved upright part on the back of the refrigerator. You will have to take off the outside vent covers to proceed.
First and most important, it has to be level
Then check that the vents on top of the boiler cover are clear, just a spider web or two inside the boiler vent tube can keep it from working.
Then try 120VAC setting and let it sit overnight. Be sure you have 120 power to the trailer.
The boiler cover will get warm. If it doesn't you can usually unplug the refrigerator from it's outlet and plug it into an extension cord and try again.
If it gets cold on 120 VAC the rest can be fixed.
Even if it still doesn't work, try the LP next, it may have a bad heating element. Again try to light
it and keep it on overnight and see if the cover is warm and the inside is cold(er)
Most often they will work on 120 VAC, but the LP section needs cleaning.
If it is hooked up for 12 volt operating you can also try that, but the trailers cord will have to be plugged in over night to keep the converter running or the battery
will just run down.
Next let us know what happens