Equipment: Nellcor - N-600
My schematic reading skills are a little rusty, but it seems power for the fan is sourced directly from Main_dc meaning it will run whenever there is dc power.
Official MedWrench Guru
There is a chip called U1 that controls the fan. That may be the bug. I would take some voltage readings before I replaced it though...if it's replaceable.
TJ Lobato | MedWrench Guru