Greetings all,

New here and to the Jeep world, but not to DIY car maintenance. I have a 99 XJ with an odd defroster issue. When I turn the fan speed to '3' or '4', the defroster door will close and cut off most airflow to the defroster outlet. Returning the fan speed to '1' or '2' causes the door to plop back into position.

I also noticed when I had the radio out that the heater core/evaporator plenum is not completely sealed to the defroster outlet. There's about a 1/8" gap around the foam that's supposed to seal the junction (actually, this opening allowed me to see the behavior noted above).

I assume, based on previous experience, that the problem with the defroster door is due to a broken or disconnected linkage inside the plenum unit, or low vacuum to the control unit. Is this a problem that can be fixed without tearing into the dash and/or pulling the plenum? Should I be looking at making sure the plenum unit is installed correctly, based on the gap I see? I could fix the gap with extra adhesive-backed foam but that sounds like a hack job.

Thanks,
Jeff
'99 Cherokee
and a bunch of other Mopars

 

check all the vacuum lines under the hood. Their notorious for dry rotting. That would cause weak vacuum to the actuator therefore making it unable to hold the duct shut all the way when the fan is turned up to high speed.