I built a pretty basic quick read thermometer as I follow this book to learn Arduino and it was working great. It is 67 in my house and it was reading 66-67F. So I put it outside where it is 45F, it continued to work fine for about 30 min then it just started to go crazy, the on board LED started to blink, the temp was all over the place 42 - 60F. I figured the operating temp of an ardiuno was pretty wide range so not sure what went wrong. Any insight would be awesome. Thanks.
Some crystals stop working at freezing point. That is why a good official Arduino board should work below freezing point and a cheap Arduino clone might stop. I don't think that the crystal is the problem. Could it be a power problem ? Perhaps you use batteries and the batteries don't like the cold.