On our 96Cherokee, the A/C is hung up in the defrost mode along with the heat. I have checked all the vacum lines under the hood and all is good. Anyone had this problem, and what might be the next step to get the heat and A/C blowing on the control setting?

 

If its only coming out through the defrost vents... Then you def have an issue with vaccum somewhere..

Common locations:
AT the firewall, next to heater hoses youll find a very small vac line there(Mine was dry rotted and is breaking very easily)

Others are along the same line going to cruise control and vaccum ball that is hidden behind the front bumper.

SInce you say the lines are fine i would start at the vac ball.. and go from there.. looking for any signs of cracks or breakage in the lines.