If the item went down the defroster vent, you must disassemble the plastic ductwork under the dash to get to the item. On certain models the dash must be removed. Please consult the factory repair manual, Hayne's manual or a Chilton's manual, one of which should be available at any auto parts store for your particular model.
The heater core is inside the hvac housing behind the dash.
I also have a 2000 jeep wrangler. This year has a problem with the heater core plugging up. You can either try to flush it out, or just replace the heater core.
how hard is it to replace the heater core in a jeep liberty limated editon step by step instructions
The heater core is inside the hvac housing under the dash.
Thermostat and/or heater core may be defective
if you got antifreeze on your windshield when you turn the heater on, it's bad
About $600
Yes
Do you live in an area that you need your heater?
Heater core may be defective
Yes. It has a heater core in the dash that has air blown over it to heat the passenger compartment.
Heater core needs flushed.