What would cause the front air to blow (heat and a/c) fine in the front but not the rear of a Voyager/Caravan?

I have a 97 Plymouth Grand Voyager. The air blows fine out of the front vents, and the far rear vents but nothing comes out of the middle row of vents. I've tried every possible combination with the knobs. Is there afuse or something simple that would cause this? Also, my daughter says in the far back row, the air is not cold when the a/c is on. Not sure about this because I'm 9 months pregnant and can't get back there lol. Thanks so much for your help!