It seems not uncommon for the fan blower (for the cab heater and air-con) to break in a Fiat Ducato based vehicle.
The classic symptoms are that only the maximum speed works whilst the lower speeds 1-2-3 don’t.
In most cases I’ve read about it’s the fault of a resistor which controls the slower speeds burning out.
It was easy to find out what the item looks like to buy but less easy to find out where it is located in my vehicle.
So, when I finally located it I thought it was worth making a short video on where I found mine. I doubt whether it’s so much different across Ducatos because it lives in the ducting, close to the blower fan (the resistor is placed in the air stream for cooling purposes so it shouldn’t be far from the fan assembly).
Here are my exploits on video. Let me know if this helps and please share with any forums that have a related thread/discussion.