This is my temperature controller. It is made by Shinko. It gets input from the temperature probe and opens and closes the relay to the left. The relay provides power either to the top or bottom solenoid valve to open them. (The valve normally lives in dishwashers.) The top valve leads to the jacket, and the bottom back to the chiller. The controller has some sort of program built in that estimates the cooling efficiency of the chiller - so its keeps the temperature fairly constant - at 12C in this case.