Ops we forgot that!
We made an upgrade to the cooling fan (for faster drying).
We have placed 2x 60mm 12V big fans on the backside of the extruder, with an external power supply, and that switch is to activate the fans.
We don't use them in any print, because a faster drying means a more stable print, but also a higher risk of shrinkage cracking (in clay prints).
So just don't care about that switch :)