The volvo window switches can be a pain.. i've taken more than a few apart, cleaned them and re-assembled them with a fairly high success rate... I had to replace one entirely a while ago bcz of the exact same problem you are having... try taking all of them out ( starting with the driver's door, turn on the ignition on and re-install them one @ a time..) see when the fuse pops and try to swap in a new switch... If you try and clean up a switch yourself, pencils work really well... a nice fresh eraser wipes off oil and carbon from the switch contacts like a champ...