If the fan is intermitent, starts when you go over a bump or a while etc then is more than likely your heater blower resistor, located left hand side of the centre console (glove box removal needed to access). Post 08 models have an upgraded version of the resistor and you may see some burning on the connectors which can be cleaned up if your good with a soldering iron. Happened to mine a while back, I desoldered the board from the connector, cleaned it up and resoldered worked ever since. Pre 08 is just a metal plate which would probably need replacing. If you want to check the fan you can pop the top dash to access the blower connectors, hard wire direclty to the battery (12v, this is the current supplied on full speed via the dash controls so you will be fine), if it fires up then your blower is good.