Initial problem was no heat out of my vents. A/C works great. New radiator, recent heater core flush. Both hoses into core are very hot. 99 sport so no heater control valve limiting fluid into core, it is always flowing through it. Only thing I could think was maybe the impellers on my water pump had rotted away so i wasn't getting good coolant flow, but last night I tried to switch to floor and air came out of the floor but also out of the little vents that defrost the passenger/driver side windows. I tried to turn it to defrost and the floor turned off, it kept blowing on the side windows, but didn't blow on the windshield. This morning i was initially able to get the defrost working but after a little driving and switching modes i couldn't get it to blow out onto the windshield. And no hot air after any amount of driving just slightly warmer than outside air. Any ideas? Anybody have a vacuum diagram for a 99 cherokee sport? Any good methods for finding a leak, I traced and didn't find any loose hoses? In addition to this if I am on one of the non-A/C modes and I turn the temperature dial to full cold I get ice cold air conditioned air out of the vents. As far as i know this should just be outside temperature air.

 

Could also be climate control panel.

 

Does your cruise control work? If it dont then look for a vac line behind the battery that has a hole. Mine did same thing but my cruise didnt work also . Battery rubbed a hole in line, fixed it and all is well.

 

Had this same problem and mine on my 95 XJ was a brittle broken plastic vacuum line by the battery. There's a vac. cannister behind the bumper on the pass side. I repaired the line and it works perfectly.

 

I have fixed the heat issue. I flushed my heater core on two separate occasions. The first time i flushed it took about 25 min to backflush, reverse hoses, flush again, repeat before there was only clear water flowing back and forth through the heater core. After that my heat got marginally better. After driving another month it started to get cold and my heat would get better after long drives but took such a long time i decided to do another flush. This time i put a little more water pressure to it and a bunch more crap came out. Now heat is working great. Still having defroster "vacuum" issues. I have traced all the lines and they all seem in tact. Probably won't worry about it until it gets worse. Thinking it might just be the "molding" around the panel doors that wore off. Don't feel like taking things apart to check