I have a 2000 E320 sedan. The air blows warm on the driver’s side but ice cold on the passenger’s side. I disconnected the auxiliary water pump and pinched off heater hose going to the control valves…. Still the same thing, warm on one side cold on the other. I have taken the dash out of the car and check most of the vacuum lines that I can see. Someone said something about a separator door or something. Or maybe it was a motor that routinely goes out. Any help with be much appreciated.

My goodness. I don't think you have a problem with the doors; but you should have run a flap test before you dismantled anything.

The most likely cause of a warm left-side vent is slightly low refrigerant.