Left side blows ice cold and the right side blows luke warm.

What could cause this?

 

I think there is a single feed from behind. strange.

 

randyb;
From what you are describing, you may have a blend door in the evaporator that is not fully opening, or a split hose leading to the dash vent that is pulling ambient air into it and then out to the dash vent.
You may try running the Heater and A/C through their varies cycles, at different settings, to see if heat is coming through the vents with the same or different volumes. This may open and close the blend doors properly.
Additionally, look uner the dash behind the vents, making sure the hoses leading to the vents are not split.