The native nest App allows you to turn the fan on and configure the duration while the status is set to “Away”
However the openHAB binding
returns:
[.o.b.nest.internal.NestBinding] - Error updating data model: DataModelResponse[devices=,structures=]
Seems like the binding doesn’t know what to do when the Status is set to away and we lose control of the fan. Is there a way to maintain the same functionality as the native app?
This sounds familiar. I believe I saw an error once trying to change state while in Away mode. Could you provide your item definition to make sure it’s not something else?
I just ran a quick test. I put the Nest in Away mode and tried to turn on the fan and received the same error.
The people who designed the official Firebase API decided that is something you shouldn’t be allowed to do, but the unofficial API doesn’t have that limitation. At least the old Nest app used the unofficial, pre-Firebase API.
The shortest path to working around this limitation is an ugly one: Install my old Nest plugin on a Vera home controller (it uses the old unofficial API), and use the MiOS binding to control the Nest via the Vera. A longer-game workaround is to get the Nest API folks to remove this possibly arbitrary limitation from the official API.
I’m not where I can test this. What would happen if I set Nest to Home, turned on the fan, then set it back to Away? Would it stop the fan or continue to run for scheduled time?
Me neither! Might work? 
Yes the work around of turning it to Home then switching the fan on and switching it back to Away works.
Too bad about the limitation