So, I recently replaced the evaporator core within the hvac unit of my 04 Grand Cherokee Laredo (pulled dash, steering column, center console, etc). I thought everything went great, but after reassembly I managed to notice that air only blows in defrost mode and I can't redirect air to any other location using the power controls. If I manually reach down to the 2 actuators on the driver side, I can redirect airflow to any of the positions, so I didn't break the doors. I checked for vacuum leaks leading from the firewall to the side of the engine and also to under the battery tray just to be safe and those seem fine too. It's also probably worth noting that the cruise controls works, which is on the same vacuum line. I'm not really sure what to check next, but I assume that I either reassembled something in the hvac unit itself incorrectly and pinched the vacuum line inside somewhere or maybe whatever power connector goes to those 2 actuators isn't connected or connected properly. I'm probably going to disassemble everything and go thru step by step again to check everything but figured I'd post here in case someone had a good suggestion on anything to check first as I really hate the idea of doing that large job again.

 

Defrost is the default mode that it goes to when something goes wrong. It's a safety feature so it will at least keep the windshield clear. Is this the automatic climate control HVAC or the manual one?

 

check for vacuum leaks, had the same issue with my ZJ a year or so back, the line on the fire wall in the engine compartment might be your culprit.