I have a 99 Protege LX, and whenever I turn on the air vents, regardless of hot, cold, or AC, it tends to blow grass and dirt out of all the vents. It does it for the defroster, head, feet, and rear defrosting vents. Should I be looking for an animal nest (what my local mechanic said to do) or something like a broken tube carrying the air? I'm at a loss. Any help is appreciated, thanks!

 

Either way you would need to get into the duct work. A Haynes Manual should be helpful. They describe how to get to the blower motor, heater core and evaporator. All of those things are tied into the duct work. Most things are on the passenger side.

I couldn't find a picture of the protege but here is one of an older 626:

 

Dirt & Debris Coming Thru Air Vents - Mazda3Club.com