XJ has no cabin air filter from the factory. Some owners DIY one into the cowl intake; expect to find leaves and acorns inside the HVAC box instead.
Across all model years, the Jeep Cherokee XJ was built without a cabin air filter. Outside air enters through the cowl grille at the base of the windshield and flows directly past the heater core and into the cabin. Result: leaves, pine needles, mouse acorns, and the occasional dead vole accumulate inside the HVAC box, contributing to the famous 'XJ funk' smell. There are two practical fixes. First, vacuum the cowl drain area annually with the wipers removed - this is the most straightforward preventive maintenance. Second, some owners cut and fit a piece of pleated cabin filter media across the cowl intake at the inner fender or fashion a frame inside the cowl. Be aware that adding restriction can reduce HVAC airflow noticeably; the blower motor is not powerful. Spraying Lysol or evaporator cleaner into the cowl intake while the blower runs on full kills the mildew responsible for most odor.
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.