Extreme cold weather caution!
The solution in the cooling unit contains water, ammonia and hydrogen. Normally this solution will not freeze. However, under extreme conditions (-30C or -20F degrees or so), there is a possibility that the cooling unit will freeze. This creates a blockage and when the heat source is called for by the thermostat, an overheat condition will be caused.
This overheat will damage the boiler and ruin the cooling unit.
If you must run the refrigerator is this situation, you can put a small heater or 60 watt light bulb in the outside fridge compartment to keep the unit from freezing. If possible, turn off the refrigerator until temps moderate.
I found this article from the rv_answer_guy ...)
Start quote --- Of Special Note: Your RVs Refrigerator is very vulnerable in cold weather. Your RVs refrigerator has chemicals in the cooling unit that will gel up like diesel fuel if the outside temperature gets down too far. This will stop your refer from working properly. There needs to be a certain amount of heat in the vented compartment behind the refer for it to operate as it should. For that reason, it is important to park your RV so the back of the refrigerator gets as much southern exposure as possible. While this will not guarantee that your refer will continue to work, this will help.
If that is impossible to do or if it is extremely cold, you can open the access door on the outside of your RV and add a bat of UNFACED FIBERGLASS INSULATION to cover the vent holes in the lower compartment access, thereby slowing down the circulation of air through the compartment and keeping some of the heat in. A single bat of unfolded and unfaced R11 should be good enough.You are not trying to completely block off the vent... you Just want to slow down the movement of air through the compartment on the backside of your refer.
NOTE: Use only UNFACED fiberglass insulation as it is not adversely affected by heat sources or open flame. AS a suggested rule, place the bat in the compartment when the outside temperature gets down to and stays below 15 degrees... just remember to pull the bat out the next spring or the refrigerator will run too hot and will stop working as well. NEVER cover or block the upper vent.In conjunction with the UNFACED fiberglass bat, I've seen the use of a small shielded 60 watt bulb in the bottom of the compartment to help further provide heat to the cooling unit in cold weather as well. Just insure if you use the bulb, place it in a drop light socket with shield and place it away from wires or anything else it may come in contact with.
THE MAJOR REFRIGERATOR MANUFACTURERS FROWN ON THIS PRACTICE SO, IF YOUR REFRIGERATOR IS STILL UNDER WARRANTY, YOU MAY WANT TO FIND AN ALTERNATIVE MEANS TO KEEP YOUR FOOD COOL. The major manufacturers provide for no preventive maintenance in this area. It was explained to me that an RV refrigerator goes in an RV... Following that thought, an RV is what it is... a RECREATIONAL VEHICLE, and the use of their product was not intended for extreme cold weather operation.
Thus so, the procedure for a frozen cooling unit is to remove it from the RV and let it thaw in a heated garage or room for at least 72 hours or more and then retest it for operation before re-installing it. Why wait for it to freeze in the first place? Preventive maintenance is the key.
As a note, I've also seen owners fill the outside of the refer access panel with the grey or white split styrofoam pipe wrap. They just cut them to length and fill the three vents, so commonly seen on Dometic and Norcold access panels. These syrofoam tubes fit snug and, because they are on ther outside of the access panel, they make more room for a drop light and are seen easily so, come spring... you will remember to remove them.
So ,how do you know when your refrigerator is froze up? It is a pretty good indication that the chemicals have gelled up is when:
The outside temperature has been below 15 Degrees F or less for several days
Touching the Chimney (Commonly a silver vertical tube on the right side of the back of the fridge behind the access panel) is warm while at the same time, the absorber vessel ( a big grey or black horizontal canister sitting the middle of all of the tubes in the back of the fridge, also behind the access panel) is cold.
To prevent damage to the cooling unit, immediately TURN OFF YOUR REFRIGERATOR AND CALL A SERVICE TECHNICIAN.
NOTE: AFTER your refrigerator is froze up, the ONLY thing an RV Technician can do is remove the unit and place it in a warm place for 48 to 72 hours to let it thaw out. He must also test it for proper operation before re-installing it in your RV. -- End Quote