Ok, I feel much better knowing that he has come and gotten the food, I think everyone on the board was thinking your poor cat was stuck and starving, but it sounds more like he's in love with his new hiding spot. Either way, it's time for him to give it up and once you get him safely out, block off the vent and make sure you check for other dangerous hiding places for him. If he's a really private cat, maybe you could look into giving him a safe hiding place, like a cat tunnel or a covered cat bed.