also just realizing - possible the resting/default temp (whatever temperature it thinks your water is at) is too low. That would also cause this problem.
It's weird, nothing seems broken. Tank water temp was 81, and I set the temp to 77 to cool. In a 24 hour period, it did nothing to lower the temp.
I also did try setting the temp down to 60, with a small amount of water, and the same effect. It simply won't chill the water. I think as you and others have said, it's either a temp probe, or no freon.