Hello and welcome to JustAnswer!
This is caused by a broken driver's side blend door in the heater box. It's not that uncommon. The blend doors are the doors that control the temperature for each side of the Jeep. There are sub assemblies available for the different sections of the box. The blend door sub assembly is going to need to be replaced. This requires the heater box to be removed and disassembled. It will take 5- 6 hours of labor to complete.