it's not that easy... you need to change more than just the control panel...
i don't know if your german is good enough, but you can have a look in this thread:
klick me...
changing from manuel ac to automatic ac means, that everything that has anything to do with the ac has to be replaced... starting from the control panel, to the display, cables, airflaps and so on and so on... you can demount every part you need from a second
carisma (with automatic ac) and mount it in your
carisma, otherwise it might be easier to buy a
carisma with automatic ac
as far as I know nobody has changed it or wrote it in this forum... but if you do it, let us know...
