1998 Buick Limited External temp malfunction

My temp readout in my car has been acting up for a while by saying it's 54 degrees outside when it's over 90 or 47 when it's 80... there seems to be no rhyme or reason to it. However, now I've discovered that when it dips below 40 the a/c compressor stops automatically and today it hovered around 30 and I had no a/c... I've searched the manual for an answer hoping for a fuse or something but haven't found anything... Please help! I live in Florida and really need my A/C :-)