2000 cherokee. Heat works decent on face and floor vents.(not quite as warm as my girlfriends cherokee...?) This i can deal with. Good air flow in all four settings. Problem: When switched to either of the defrost modes, the air stays warm for 10 secs or so and then becomes room temp or luke warm. Quickly looked over vac lines and everything seems to be ok. Removed glove box and bottom door is working properly. swapped climate control with the other cherokee and no change. defrost not warm....Any help would be appreciated before taking the dash apart. thanks

 

when switching on the def the a/c compressor runs and since youre getting crappy heat the a/c cold air is overpowering the heated air thus making it cool. i would consider flushing the heater core.,some stuff to read,

http://www.google.com/search?q=flush...hrome&ie=UTF-8

 

The rad water pump and tstat were all replaced. System was nasty from previous owner using stop leak. We cleaned and flushed it. Going to flush again today to see if maybe there is still some gunk. Any ideas if this is not my solution...? again thanks

 

flush the heater core by itself, if you wanna confirm my diagnosis pull the a/c relay out thereby disableing the compressor. if the air stays warm you have confirmation

 

Like kennzz said. It does sound like your heater core may be plugged. Flush it really well by its self. That should take care of it. But, You did say that the PO used stop leak in the cooling system and it may not flush correctly and my need to be changed out.

 

working much better. going to flush it again in a couple days. thanks!