If you get under 20 at night, or above that but without being above freezing during the day, or just barely, you are risking getting things broken up. Outside showers are one of the worst, followed by exposed pipes and drain valves, and after that... almost any part at all.
But if you have a modern C with it's drain pipes all enclosed, and some ducting to all cabinets that have water lines in them, put your furnace on at 50 and keep your propane up so it stays warm.
If it's an older unit, don't risk breaking it for want of a little smelly pink in the lines, learn on here how to do it right and then clean it out when you are into a safe place.
Above all, study all the methods here, there are so many places people forget to winterize, and if this is your first one, it's a big learning curve and you might as well go for it now and keep on reading. Lots of pitfalls and traps along the way will give you anxious moments.
