Originally Posted by My_1st_TJ2003
Was the system burped if not it vary simple take ur radiator cap off jack up just the front only leaving the cap off and let it run 4 about 30 min tht way u can have an air pocket in the system start small simple n free to do in ur drive way
I would be willing to bet it's air in the heater core or some kinda of blockage in the line/core itself. Word of advice though, when you let it run with the cap off you will more than likely get a mess in the driveway.
If burping the system doesn't work you may want to look into the mechanicals (Blend air door, hvac controls, etc.)