AC3 temp 120 degrees

[DrHarryLopez]

AC3 temp reads 120 degree but on the datalog it reads 18.5

I reset the AC3 controller but the readings remained the same.

My chiller kicked on however I manually shut it down.

The Tank temp is current 77

Do I need to buy new probes?

[kenargo]

Yes, the probe has gone bad.

[ciphros]

Another thing - a good practice is to put in an extra statement that kills the chiller in a situation like this. Use an additional if Temp statement that has a temp higher than you expect to ever see in your tank and have that turn the chiller off (see the best practices thread stickied in this forum).