Temprature sensor issues.

Arduino mega R3 Hey guys. I have some trouble with my temperature sensors I have one managing my led unit temperature that turn om fans of certain temp is reached, and then have n water temperature sensor that only reads water temp

my problem is that the sensor readings are jumping around between -127(undetected) and 85deg. that in turn messes around with my cooling of my led units.

does anyone maybe know how to fix problem.I do not know how to change the code already in use and if it may be a conflict.. Please help