I replaced the heater core in my 02 grand Cherokee overland. Now the air only blows at my feet. What can cause this to happen? And how can I fix it?

 

My first guess is a problem with the blend door. I have not dealt with them on a Grand but in most vehicles they are controlled electronically to move the door to one position or another. Either it is stuck or malfunctioning or the wire connector got unplugged.

 

That is controlled by a vacuum hose. Try this video first. The blend door is usually a temp control problem. Though in the video, he is stuck on defrost it could be your issue.

 

But the dual climate control blend doors do have about a 100% fail rate. When you had the dash apart for the heater core, that would have been the best time to inspect and replace that.