Passing Gas (Propane you louts!)
Ammonia refrigerators are very different critters from freon based ones. If you arrive at a full hookup spot and want to turn your refrigerator on using electric, you can do so immediately - and ditto for running it on propane if you're camped and boondocking.
BE AWARE - If your unit is at room temp. and you plug it in OR fire off the burner your freezer will start to get cold first, but it will probably be a whole day before the refrigerator gets cold. Your food doesn't have to spoil while you are waiting for the ammonia to slowly lower the temperature - you can chuck a block of ice, or a bag of ice cubes or even some dry ice into the refrigerator and use it as an old fashioned ICE BOX while the cooling process starts.
Ammonia refrigerators have been around since the 1870's or 1880's. The industrial sized refrigerator was first used by the beer brewing industry... and took quite a while to become a household appliance except for the very wealthy.
In eastern Virginia almost all of our major tunnels and bridges do inspections on RV's to make sure that propane tanks are OFF while traveling. And while fire is a remote possibility most people who DO use propane for refrigeration while on the road - recommend that you turn the gas OFF while refueling your tow vehicle. A buck spent on a bag-o-ice seems like a reasonable safety procedure, does it not?
Today is a gift, that's why they call it the present.