Yes turn on at that but still off at 25.6 (nominal value)I think you should observe the Chiller outlet turning on and off at ~26.4C. Maybe on at 26.4C and off at 26.3C.
T = 25.6 + (0.83)(0.95) + 0
Whats happens if you have the hysteresis to 0.15 C. If your works as it should - it should turn on at around 25.73 (with @ingchr1 calculation schema.
I still think it is something else that is wrong.
@Gaël
Sincerely Lasse