I have a 2001 Ram that was sitting for a couple of years and I think the mice got into the vents.When I turned on the fan there was a humming noise and stinky air was comming out and then the air stopped so I'm guessing Its all blocked up but have no idea how to clean it out.

 

Download the free service manual from the FAQ/DIY section and remove the HVAC box and clean it out. replace the heater core and AC evap core while you have it out.

 

the fan motor is right under the passenger side glovebox, real easy to reach. just replaced mine this weekend. so if your lucky the stinky smell is from some sort of mold growing in the hvac box and humming from bad motor. take motor out, spray lots of lysol into box, replace with junkyard one, and call it a day.