Just thought I should add my experience with aux fan woes. Both my fans on my 1990 300e were constantly running once I turned on the ignition. Even though the ac is not even working. I ordered coolant temp sensor and the black relais behind the fuse box. Turned out I didn't have the correct socket for the temp sensor but I replaced the relais (0015426819 in my case) and the fans are no longer running constantly. It remains to be seen wether it kicks in if the engine should start over heating. I just replaced the fan clutch and without ac too there is not much chance for that here in Norway. Anyway.