My friend Mike Carlson, an ace auto-restorer, noted that old AMC Ramblers had unusual air-conditioning controls.
"They had the usual low to high settings and a very optimistic setting for 'Desert only.'"
Hmmmm. I've lived in the Southwest, and I recall that home/office cooling systems down there employed a design different from traditional air-conditioning. But it's hard for me to believe that AMC equipped its cars with dual AC systems in the 1960s.
You probably won't be able to make it out in this photo ("Desert only" -- over on the bottom right), but it's the best I could find.