so whenever i turn the heater/ac on, i get blasted with stale and smelly air. ive sprayed the vents with vent deodorizer from napa, but it just covers it up for a few days. i think the problem lies in the ducts themselves, where mold has built up and such. How do i get into the ducts though to thoroughly clean them out?

 

Pull the dash.

You've got a heater/AC box that controls where the air blows, then you've got a large ducting box behind the dash which the heat, vent, and defrost ducts attach to. You can get the defrost vents from the top by removing the dash pad, and you can get to the HVAC box under the passengers side of the dash, but it sounds like you've got something in the ducting that shouldn't be there, like a dead mouse. You're going to have to track down the source and remove it, and even then you might not get rid of the smell.