If by grounding pin A4, the fan then blows air, then the fuse, fusebox and enabling of 12V(which is only enabled when the engine is running) are all working. This is good news as the rest is relatively simple.
Note the enabling of 12V was the only bit I didn't reverse engineer as it was working for me too.
See post: https://citroenc3owners.com/citroen-c3-q ... -t879.html
to see the scenario that I had. I very much suspect you have a similar or the same problem.
Did you get a replacement control unit? Do you have the capability of confirming the replacement control unit works? Do you know how to remove the fan motor? Do you know how to use a multimeter? I can explain how to do all of this, although removing the fan is a bit of a pain.
Does the fan work on setting 4 of the replacement control unit?
Basically my fan had gone low resistance(note it would still blow air fine with 12V across it, it was just using lots of current and hence the reason it blew the control unit and resistor pack). This then blew my control unit and my resistor pack. I can send you a drawing of how its all connected if that will help you.
I got a replacement fan motor, replacement control unit and a replacement resistor pack. With the exception of wires(which might be burnt out, but I doubt it) there is nothing else to the circuit.