You may need to help the fan get moving by turning the blade a little.
Past posts on the subject in-car fan resuscitation -
http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,296087/highlight,/sid,73b0192de3fceb93d1f6ffff3bab000d/
http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,333182/highlight,/sid,6fd4f31f1fb975c808e4d0c74fc2a736/