Thank you for using Just Answer for your needs. Does the air conditioning cool equally on both passengers and drivers side?
So the only concern is that the heat does not work equally on both sides, correct?
This is definitely an odd concern. The problem does not sound at all like the heater core. When the Dealership checked it out did they check and watch the blend door and air select servos for movement?
Yes, that is what I am thinking. Them hooking the Techstream scantool up is not a great way to tell if the system is operating properly as the data and diagnostics is extremely limited. It's not like the engine computer diagnostics.
What they should have done is taken the lower dash panel out and disconnected the servos, then manually adjusted them to see if the operation changes. Most likely one or move on the doors is not operating fully or is stuck due to an internal air box fault.
If it is the servo then yes. If it is found to be the internal linkage then the box itself will have to be replaced or at least opened and checked to see if it can be fixed. If the box itself needs replacing then it will be expensive but just the servo will run only about $150.