Sucks bad huh? I just had one of these in the shop last week. I put a new fan motor and power stage in it and all is well. We had problems with the 850 when it first came out doing the same thing and the "official" fix from the Swedes themselves was to put both a power stage and blower motor in it. Their explanation was that it was actually a bad power stage that burned up the motor and if you put just a motor in it it will work but eventually it will burn up again. You can try just a motor and see if it works, and it will, but if it burns up you will need to do both. One thing though is that the blower fan and power stage are different in an S70 from the 850 so you might be able to get away with it.
Hey look at the bright side, at least they did not put the power windows AND the A/C on the same fuse like they did in the 240. My daughter started driving her younger bros car yesterday because her a/c is out and guess what? Bad connection at that fuse and she had no a/c and no power windows. She was just a little bit pissed off when she got home yesterday!!

Mark