Hello and welcome to Just Answer. My name is Denny; now let me see if I can help you with your Jeep question.
There is a blend door inside the HVAC unit, that breaks, and causes this. You need to remove the entire dash, and then remove the HVAC unit, and disassemble to get to the broken door.
This is a big job, and quite difficult; I can send you some removal procedures, if you want to tackle this yourself.( if you want the instructions, you need to tell me if you have duel zone climate control or not.)
WARNING: Before servicing the steering column the airbag system must be disarmed. Failure to do so may result in accidental deployment of the airbag and possible personal injury.(refer to 8 - electrical/restraints/driver airbag - removal).
NOTE: Use care not to break off the tangs on the shrouds.
CAUTION: Do not turn the steering wheel more than 90 degrees or damage to the clockspring may occur.
WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNING) and (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - CAUTION). Failure to follow the warnings and cautions could result in possible personal injury or death.
WARNING: Disable the airbag system before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Disconnect and isolate the negative battery (ground) cable, then wait two minutes for the airbag system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the airbag system. Failure to take the proper precautions could result in accidental airbag deployment and possible personal injury or death.
NOTE: The HVAC housing assembly must be removed from the vehicle and disassembled for service of the air inlet housing, air distribution housing and the A/C evaporator.
NOTE: Take the proper precautions to protect the front face of the instrument panel from cosmetic damage while performing this procedure.
NOTE: LHD model shown in illustrations. RHD model similar.
NOTE: The HVAC housing must be removed from the vehicle and disassembled for service of the A/C evaporator.