I can't actually get my cooling fan to work see
This thread and I guess this may well be a problem with my understanding of Marlin, but I was also wondering...
How clever is the cooling function? does it cool more when layers have less extrusion?
My first 3d printer experience was building a tronXY P802M for a friend. The part cooling fan on this seemed to have a little life of it's own changing speed all the time. Even "off" it did a bit spinning occasionally (!?).
I presume this printer runs a closed version of marlin on a RAMPS like arduino board.
There seems to be little (any?) setup for part cooling in Marlin.