Hi ThomD - take a look at this thread:
http://www.expeditionportal.com/forum/showthread.php?t=7268&highlight=zone
I didn't find mine worked very well before I did a simple modification (detailed in that thread). Now it cools to the same temp at my Engel and I am extremely happy with it and wouldn't part with it for the world. I love being able to open my fridge in two sections to get at things!