At very high elevations the ambient temperature is often cooler, so you may be able to get by with one A/C. That’s been our experience traveling through the Rockies. That’s not to say you may not need to adjust the carburetor anyway, just that you may not need enough power for both A/Cs at same time.
Regardless, with thinner air at higher elevations, non-turbo engines can lose about 3.5~4 % power for each 10,000 feet. If camping on North Rim of Grand Canyon at 8,000 feet, as an example, it becomes significant.
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