Edit to MIne Above:
Actually, my thermostat is a mini-computer; if things get below XYZº, it moves to heat; if it gets above ABCº it goes to A/C on it's own; it also has some sensor that regulates for RH; I think if it gets above 74º it goes to A/C and if I remember correctly it automatically goes to heat if it gets below 64º indoors; of course it has manual override, but I really never use that unless it's 65º indoors and snowing like crazy out (Yeah ...) ... and if it gets cool inside and the heat hasn't kicked on, I've got 2 fireplaces (which keeps the utility bill way down in the 2 weeks of winter ...)