Hi! The AC ducting on your Intruder is controlled by engine vacuum. The default position is the defrosters. My guess is you have a vacuum line off. It will take some detective work but the Ford chassis (I'm guessing it's a Ford) uses a vacuum cannister and it's under the hood somewhere. It's black and should be round about 6 to 8 inches in diameter. There should be two hoses to it. One from the engine and one to the dash. If you find it, you can pull the hoses off and see if there is vacuum. The larger hose usually goes to the engine. That should have vacuum when the engine is running. The smaller hose that goes to the dash won't but the fitting on the cannister should. It's just a storage container to keep the vents where you selected them while engine vacuum is low (like going up a hill).
You may even get lucky and be able to hear the leak...at least if it's under the dash. One final thing. If you can, look under the dash and you should see at least one of the vacuum servo's that move the divertors. Maybe the hose just got knocked or pulled off of that.
2002 Damon Challenger 348