On several Ford Motor Co. products I’ve owned the relevant settings are “A/C” (outside air) and “A/C Max” (recirculated air). For a long time I thought I was saving energy (and gas) by using A/C instead of A/C Max. It wasn’t until I read the owner’s manual (and who does that?) that I realized I was wrong. It takes more energy to cool the hot outside air than to re-cool the already cooled inside air.
I’ve never noticed the air getting stale or anything, even on long, cross-state kind of trips.
A little off-topic, but I once worked on an airplane that had some instruments that were cooled with liquid nitrogen. Nitrogen isn’t poisonous but if it leaks it could displace all the oxygen in the air (which is a bad thing) and your body has no way of knowing this is happening. As a consequence they had little oxygen meters all over. The first few days I was always checking the meters to be sure I could still breathe! I kept getting short of breath – I was sure we were all going to be asphyxiated! It took quite a while to calm my irrational fears, but I wasn’t used to having to check if there was any oxygen around.
“non sunt multiplicanda entia praeter necessitatem”
– William of Ockham