It could be the recirculation flap mechanism.
I had the 1/2 gear part that operates the recirculation flap break. It closed recirculation flap all the time, even when the knob was not set on it.
This gear is a half gear located under the dash, near the center hump on passenger side. You need to remove the cover & look for broken plastic.
I did not change it myself but the mechanic knew right where to go & as I watched he pulled out the part.
It looked fairly easy to check & replace.
2015 WK II 5.7 Overland, Offroad Group II,- 2008 WK Limited 3.0 CRD, - 2003 WJ Laredo 4.7, - 2001 WJ Laredo 4.0, - 1999 WJ Limited 4.7-