The late Vanagon air conditioners probably have 12,000 to 18,000 Btu/Hr.
capacity. 1 to 1.5 tons. If you look at regular air conditioning systems you
are looking at about 1,600 watts running for some of these units. Just a bit
over 2HP. And that usually incudes fans for both the evaporator and
condenser. Engine driven systems are often less efficient due to the engine
speed being determined by the driving needs, not the AC so the system has to
work with that. The compressor needs to be oversized so that the system
works at idle and low speeds which ten in turn becomes massive power losses
at high speed. This loss is made even worse with systems that are over
charged and/or contaminated with non-condensable stuff, (compressor oil),
air, etc. Probably 3 Hp is the real loss not counting the electrical
demands. But even if an electric AC system needed only 2Kw, in the 12 volt
world that is still 1.47kw.  111A/H at 13.2 volts. Taking into account the
inefficiencies of small alternators you may be looking at 3 to 4 Hp for
that. Now you need some big belts to drive it.

Figure out a way to get a window unit installed under the back seat and get
a Honda 2Kw generator to run it. In Europe there are 12 and 24 volt air
conditioners used for trucking and RV's. May someone can import them.

Dennis