Heater CORE, not coil. The core is plugged and needs back flushing or replacement.
Leaking heater core
Vent bypasses heater core when open,it is for outside air only...I know this because I just replaced heater core.
Because your jeep wrangler is over heating, you must have a sensor in the dash not working If that smoke is steam, the heater core is leaking and in need of replacement.
Check that the linkage that controls the damper is connected and working. The linkage is just above the gas pedal.
Check the heater core, it is probably bad. It could be heater hose connections to the heater core, but I would bet on the heater core going bad.
smoky mist coming from the heater vents.
The heater may not be on - but the fan still blows air through the vents when they're open !
There are heater doors on the heat blower box that direct the path of the heat. Apparently the heater door to the floor vents is stuck closed.
check radiator cap for proper pressure first.then check clamps at heater core
heater fan broken.
Your heater core is leaking, Need to REPLACE HEATER CORE.
Leak in heater core. Replace core.