I have a 98 grand cherokee Laredo every setting on my switch panel blows thru the defrost vent only so i replaced the switch panel in dash, still the same, ac works good but even on defrost heat is Luke warm but my first concern is why does every setting only blow through defrost vents

 

There is a vacuum reservoir built into the bottom of the battery tray, make sure the vacuum hose is connected to it and that the line is not broken. Does your cruise control work? It is tied into the same vacuum line.

 

I'm pretty positive the cruise works, I'll check that line now, if its all good what else do you think it could be, i believe the heat issue if a sticking thermostat I'll change tomorrow

 

The line running under the battery looks fine

 

Could the linkage for everything be unhooked or the servo control that moves it be bad?

 

I been thinning about it, earlier when i replaces the control switch in dash it had the write harnesses plugged in but there is anotherspace for a forth connector but no harness to plug into it I'm wondering if that's the problem

 

Posting via phone is horrible sorry I'll post on my tablet shortly

 

Sounds to me like the infamous blend door problem. My 97 ZJ did the same thing and the blower didn't put out much air. On high it sounded like a tornado in a keyhole.