I was already familar with the basics of the ammonia cycle fridge that
our Westy's have in it. I was undecided, however, on whether or not it
was an Einstein design fridge (yah, that Einstein.) I also didn't
understand the improvements that Einstein had done to the ammonia
cycle fridge.

Now I do. Sometimes it takes the right teacher. It's actually a very
cool augmenting of the ammonia cycle. So first to the basics of the
ammonia cycle.

Ammonia is an interesting substance. If you heat it up, only slightly,
it will vaporize and in the process of vaporizing, it will absorb
tremendous more amounts of heat. That's the basic principle used in
the Dometic fridge and in many other 3 mode fridges. To augment this
the heat chamber usually has a constriction on the exit, so that
ammonia gets pressurized as it is heated. This enhances effect of the
vaporizing of the ammonia liquid.

Einstein's enhancement was to put Hydrogen gas in to the cooling
chamber. Why? Well, because it lowers the gas pressure. And, as most
folks know, liquids will boil at lower temperatures at lower gas
pressure. So it means you have to supply less heat to the liquid
ammonia in order to vaporize it, and hence you can get even lower
cooling temperatures. It is also a very very energy efficient design.

There are folks that are investigating the Einstein design once again,
using different gasses to see if they can make improvements.