I think they want to check the temp (presumably, w/ temp sensor?) then use the pot to tell Arduino to tell the chiller by how many Celsius degrees to change the temp.
Does "RF" room mean....."Radio Freq. Room"? ..."Refrigeration Room"? Dunno?
So... you want to use Arduino as a thermostat?
One could map the pot voltage to a certain temperature range. However, if you want to specify a particular delta, buttons (or encoder) may be better choice.