All Cooling units that have fans installed on the rear coils have this type of control switch to operate the fans to give the needed air flow through the coils.
This fan is set to activate at a lower surface heat temperature than the OEM's.
  We feel it is better to have, when needed, the fan air flow starting  before the cooling unit preformance starts to fail.

This switch is use to replace the OEM's installed switch at the time of failure or to be added to refrigerator coils when adding your own fans.

None operating fans, either from bad switch or bad fans, are the most common problem an cause of early cooling unit failure.

We have both fans and fan switches in stock.
The location of the switch is not a manitory location.  You can mount this switch any location you feel to best serve your fan activation, according to the surface temperature.  Cooler the surface, the longer and more heat build up in the coils.