Some of the newer Norcold and Dometic fridges have no pilot, and use direct spark ignition (lower gas consumption, too). Not sure how small they go with this feature, but the flame sense and auto shut off/alarm on the new units make 3-ways redundant, you just have to remember to TURN THEM OFF
, when re-fuelling. They were always marginal on 12V anyways, and you better turn to gas if your engine would be off for more than an hour, or 'Hello,AAA?' The original fridge in my Layton was a 3-way, but it used the same 'micro' switch for either 115v or 12v, and the current at 12v (almost 10 x) cooked the switch. Then, instead of correcting the problem by replacing the switch, and slaving a relay for the 12v heater supply, they added another thermostat (at the back) and disabled the 12V. As the unit was pilot light
type, you couldn't depend on it (almost never) to stay lit on the road. So, on a trip across the continent, I installed a 400watt inverter, to operate the fridge on the road. This remedy worked fine until the element shorted and blew the inverter. Then I operated it on propane
only for the balance of the season, replacing it with a new 'Norcold' 5.5 cu ft over the winter.
BTW, I also use a 'CPAP', but mine is a two-piece unit, with the pump running at 12v(DC), and only the humidifier requiring 115V. I run 4-5 days on battery
, without recharge, when 'Booning'