2004 Jeep Cherokee

What you are looking for in this case is a vacuum leak. The vents are actuated by vacuum. When there is a leak, everything comes out the defroster. Check for leaks under the dash, follow the supply hose from the controler through the dash and to the engine. NOTE: Chrysler uses plastic tubing which connect with rubber ends. If there is a problem, the plastic will be cracked and not easy to find. I always start at the controler in the car to see if there is vacuum making it there from the engine. From that point, I know which direction to check, toward the engine or under the dash.

Let me know if you have questions. Also, with the engine running, you may get lucky and hear a hissing sound where the leak is.

Joe