The way a refrigerator or freezer works is that the refrigeration unit kicks on when the temperature rises above its setpoint. In many cases, this may just be set with a nob that has a blue bar on it. When the unit senses it is back to or just below setpoint, the unit kicks off. Therefore, if the temperature on your controller is below the refrigerator setpoint, the refrigerator will kick off before you get cool enough. You should set your refrigerator temperature as low as you can. If you are trying to control your freezer to a specific temperature, you may need to adjust it with each temperature move, unless you have one of those fancy dual unit types. If you only care about the refrigerator portion, then DWHAHB. If you just want it as cold as possible, set the differential to its highest setting, set the fridge temperature to the highest setting you will use, stick a thermometer in the freezer, and see how cold it stays. If it stays below about 30 degF, you have a freezer, though not the best. If not, you have a really cold storage spot that sometimes gets to freezing.