Can a 2-way RV fridge be converted to a 3-way?

Dear RV Doctor:
gary-736We just replaced our Dometic refrigerator with a new one. On our old refrigerator we had an aftermarket 3-way switch put in (AC, DC, Propane). That way we could run our fridge on DC while we drove. Now I am told I can only use propane or electric and the fridge is off during travel. I can’t believe stuff stays cold enough. We often travel for several hours at a time. What is the problem with using DC while driving? The batteries charge while driving. Is it possible to put in an inverter? —Edie T., Kent, WA

Dear Edie:
Indeed, the two major manufacturers of RV refrigerators produce both 2-way (120-volts AC and propane) and 3-way models, which includes a 12-volt heater for operation while the vehicle is in motion. The 12-volt DC mode of operation, however, is considered a “maintenance mode” only. Realistically, the refrigerator’s interior compartments must already be cooled down and the food chilled prior to setting the unit to the 12-volt mode. It would take too much out of a typical battery system to cool a warm refrigerator down from scratch on battery power alone. In other words, the drain on the system would be a greater load than most battery systems could provide before becoming depleted. By the way, I’m not aware of an approved aftermarket kit for adding a 12-volt DC heating element to a standard 2-way refrigerator and would be quite hesitant about using one anyway. For correct absorption cooling operation, the sockets for the heating elements must be properly welded to the cooling core and this can only take place during manufacture.

Yes, you could add a dedicated inverter to power the refrigerator on 120-volt AC while driving but that, too, would require proper sizing of the battery bank. In my experience, simply getting the refrigerator (and the properly stowed food), as cold as possible on propane or shoreline power before heading out, and then avoiding opening the doors during the day, will usually keep everything cold enough until you can fire up one of the other modes once you stop for the night. The frozen T-bones and lobster tails should not defrost during that time.

If you really must have the refrigerator on while driving, but aren’t confident using propane while going down the road, then the addition of an inverter and a healthier battery bank might be the most economical option; certainly less than swapping out the refrigerator again for a 3-way unit. I’m curious as to why the dealer simply didn’t sell you a 3-way model to begin with.

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Rusty Nayl
Rusty Nayl

I think you may be wrong regarding the size of the batteries and vehicle charging system. On most that I know, Dometic refrigerators have a 120vac 325 watt heating element, which is very adequate for cooling. The difference is on the 12 volt DC element is only 125 watt, I think., which will not heat the boiler enough to provide adequate cooling. Why the design engineer chose to make this element small is beyond my knowledge. A 325 watt element at 12 volt DC would draw less than 20 amps. 20 amps DC is much less than the maximum charge… Read more »