The ATC-800 only goes down to 5C (unless there's a newer version). You can either bypass the ATC when you want to lager/cold condition or you can get a different controller - there's another one some of the guys use but the name escapes me (PC10?). My fridge gets near enough to 1C if I bypass the ATC, it's a while since I checked the temp but it was in or around that range.
