Passenger side stays cold as does rear unit. Have to stop, cut off engine wait 3-5 seconds and start again. everything is fine for about 30 minutes of driving.
Not familiar with zone question. both front thermos are set to same setting. Only driver side dash outlets are putting out very hot air.
Assuming you do not have separate controls for the driver side and the passenger side, then my guess is it is a vacuum problem. You may have a vacuum leak or just weak vacuum. On most cars the heater controls are managed with vacuum. A small leak can cause what you describe. Let me guess. Right before you notice the heat, you accelerated, like maybe from a traffic light or to pass a car?
I read you reply so you do have separate controls. My money is still on the vacuum issue, but just not as strongly.
Good Lord Star; give this nonsense a break.
Listen to Mr. Meehan instead.