I had the same questions when I bought my 84 a few months ago.....Its a kinda strange setup but I now also understand why they did it that way.....
Essentially, the heat flow is controlled by the red rotary knob & 2 levers between the seats. There is a housing around the exhaust manifolds in the engine compartment (under the engine) called heat exchangers. They are connected to duct work that route through a fan also mounted in the engine compartment. You can see the fan on the left side of the engine when looking at it with the engine lid open. Its the large black stuff. The rotary switch controls this fan (and 2 other fans located at the drivers & passengers foot-wells) and it pushes the warm air toward the cabin.
The levers open a flapper valve that is in the ducting between the fan & the cabin of the car. Each lever controls a flapper valve on its respective side of the car.
If your heat is constant on the drivers side, I would think either your lever is up (on), the cable has hung up somewhere, or your flapper valve is stuck.....
Here is a very good thread that explains the heater function both auto heat & "manual" heat.
Inane heater controls
It seems that Porsche thought it would be a good idea to have 2 separate systems to route air in the car. One for heating & defrosting & one for cool air movement.....I say cool air as there is much debate on the effectiveness of 911 A/C and if it should even be installed....but's that for a dozen or so other threads....
The owners manual does have a very good explanation of how it all works. Let me know if you don't have one and I will scan the pages of mine and email them to you....
And welcome to the club......you must, in all good conscious post some photos of your "new" car.....
Having owned 64 cars so far, this board is by far the best single spot resource for any vehicle I have ever seen.....the people here will bend over backwards to help in any way they can......You will be spending quite a bit of time on the site.....
Chris