I plugged my fan and the freezer (Keezer) in to a power strip then the strip into the Johnson... this way my fan only comes on when the Keezer is on...
Photo of the power strip, and the fan. The fan is out of a frig, it is sucking the air from the top and pushing it to the bottom of the keezer.
the power to the fan is plugged in to a power strip with the freezer, then the strip is plugged in to a Johnson temp control... when the freezer comes on the fan does too.