Today I installed a fan into my new kegerater.
A fan helps maintain a constant temperature throughout the fridge. The converted chest freezer I am using cools the fridge with plates on the outside. The air is quite stagnant in the fridge, so the cool air settles to the bottom. This can create a temperature gradient of the beer within the keg, leading to foamy pours. The first pour is a little foamy right now.
The solution: a fan. This DIY post describes an example of installing a fan, and outlines the need for one.
The Finished product
I used to angle brackets to mount the fan to the collar. Currently the USB wire for the fan just rests on top of the lip, but does not seem to disrupt the seal between the lid and the lip.