Chest Freezer Temperature Controller Question..

So, this whole brewing process is fairly new to me, I've recently bottled my first batch of an Amber Lager, with an Oktoberfest on it's way to be kegged.
Now, I recently purchased a Kenmore 5.1 cu. ft. chest freezer and it works great, along with that purchase, a Johnson Temp. Controller, seen here; http://www.amazon.com/Johnson-Controls-A19AAT-2C-Temperature-Controller/dp/B0002EAL58.
Like I said, this is new to me, and my question to everyone here is if the chest freezer is supposed to be off (or seemingly off)? I'm not too sure how this Temp. Controller works exactly, obviously I know what it's supposed to do/what I want it to do, but should I be concerned or not? I have a thermometer in the freezer that's reading about 39 degrees now, and the temp. controller set at around 38 degrees fahrenheit.
Am I overreacting? I set up the controller roughly 7 hours ago.
Simple question, how do these darn things work, in plain ol' English?

While I don't have an external temperature controller, from what I've read on these forums, it seems to be working properly. The Johnson controller overrides the power to the freezer. Basically, when the temperature hits "roughly" 38F (where you have it set), it removes power to the freezer. Power will turn back on to the freezer when the temperature rises to the factory set differential, which I believe for this model is 3.5 degrees. I.e. the controller removes power to the freezer at 38F and will restore power to cool it back down around 42F. These temperatures are all "rough" because the analog controller is not as precise as the digital ones.