<< Are they allowed to drive around in cars with a/c? >>
It really depends. Some areas, where there are very few people spread out over long distances (rural and semi-rural) a car is about the only way to go. In cities, where the population is more densely proportioned, bicycles are used more, and they will occasionally get rides from church members who offer.
Of course, then there are areas (usually in other countries) where they won't have bicycles and have to walk everywhere.
But yeah, on those hot days it can be kinda tough.