I have a 2001 jeep cherokee xj. First off let say it all started with it working on full blast, changed the resistor, and it blew out. Today i went and exchanged resistor and bought a relay. Works okay now but feels like it doesn't blow as hard as before. besides that though i tried to fix it where it would work on everything instead of just defrost. I changed all the vacuum lines under the hood and the colored ones going from the back of the panel to behind the glove box where they disperse different ways. still didn't work and then i went to mess with them under the hood and ended up pulling the little one out of the firewall. Im in the middle of pulling my dash to reattach the little one i pulled through. but what is my problem. all vacuum lines under the hood are ok, it has to be in my dash somewhere? I'm ready to pull it and go get new everything...

 

so everything was working properly, and you then changed out the resistor and started having issues?

 

Have you checked the vacuum ball under the front bumper on the passenger side for cracks?