A/C problem

Ever since I got my 87 jeep cherokee, 4.0L, the A/C has only blown air (hot & cold) on the defrost setting and will not change no matter where the slider is set. Does anyone have any idea what could be causing this and how to fix it? I was thinking vacuum lines, but I'm not sure.

The vacuum lines on the back of the a/c controller is what determines which flaps open and close to route the air through. Easiest place to check is the back of the controller and make sure it's plugged in and see if any of them are damaged then if it looks fine under the passenger side of the dash is where they meet the unit make sure that someone hasn't accidentally kicked one loose or the whole thing.