Remember ROVAC? The working fluid was the air blown out into the passenger compartment (a similar cycle to what the air conditioning on jet airplanes uses. It worked, but the compressor and ducting were bigger than the car's engine :-) Jets can use the air cycle because they just bleed the compressed air off the jet engines themselves right before it enters the combustors, cool it in a heat exchanger, then let it expand and get REALLY cold on the way into the passenger compartment.