How to use D9 as print fan with Mixing extruder?

Hi there, 

Just like the title says, how can I use D9 as print fan when using a mixing extruder? Because I use a mixing extruder I have to enable a 2nd extruder, but because it's an mixing extruder, there is only one hotend. Now I have D9 free for a print fan, but the software doesn't allow it, because I enabled an 2nd extruder.

Is it possible to change the firmware somewhere so I can use D9 as print fan?

Thank you in advance!


  • You need to set EXT1_HEATER_PIN and all follwong to -1 so they never get set. Espcially D9 is critical in ramps boards
    since it is defined as D9 overriding fan if not changed,
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