Steve:

Gas refrigerators (still made in Evansville by Robur, who bought up the Servel patents in the 60s) work by absorbtion chilling, not expansion.

What happens is that ammonia and water, when mixed, absorb heat. Quite a bit of it, in fact, enough to drop the temp to well below freezing. The mixture stays liquid from the freezing point depression of water from the ammonia -- temp is something like -15 C.

In the chiller unit, the water is passively circulated by differential heat from the absorbtion section to the boiler, and the ammonia is separated by boiling it off. The ammonia is condensed from vapor in the condesor at the top of the rear of the fridge, and the water is cooled back down in the lower part of the heat exhanged, where it runs back into the absorbtion unit. Liquid ammonia drips into it from the condensor, and it cools off.

Requires about 1000 psi internal pressure for this to work, as I remember, always a problem and the major reason why you don't see ammonia chiller systems on cars. They would be very cheap to run, as the heat required is freely available in either the coolant or exhaust. No way to keep them from leaking out, and the ammonia is too toxic.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!