I recently purchased a 99 Cherokee Sport. The A/C control is not working properly. It seems the air always wants to go through the defroster no matter what the knob is turned to. Sometimes it will come out through the other vents for a short time but eventually it circulates back through the defroster. It sounds like the vents aren't opening / closing correctly. I've heard this might be some kind of vacuum leak. Has anyone else had this issue? How did you fix the problem? I previously owned another 99 Cherokee Sport and had the exact same problem but never bothered to fix it. Thanks for your help.