I suppose late than never. Just had the same problem with my 280SL. On ignition on, fan can be heard and felt, despite being off on the switch. Still had it's four position fan speeds. Electrician had a look and found a green wire with a white trace connected to the air conditioner switch adjacent to the blower switch. This wire had no contact/connection with the fans black switch block and was piggy backed onto the air cond switch by a double male connector. Apparently Volvo fans run on start up and it appears it was a previous owner mod. The elctrician completed his trade in Sth Africa on Mercs, sp knpws them inside out. A little mad for his experience. Anyway disconnected the wire and no more fan problems. The green/white wire is hot, so was taped up. Everything else is working fine, so it's function is a mystery. It may not help, but it's one easy check to end the frustration.