You are right.  There is a heater box under the back seat and that left
hand switch is supposed to control its speed.
  Under the seat on the left side of the assembly as you face it there is a
lever on the valve that controls the flow of hot coolant.
Have fun,
Larry A.

On Wed, Sep 4, 2013 at 7:58 PM, Eric Caron <ecaron1@comcast.net> wrote:

> Hi listers,
>
>         I've noticed a few comments off and on about the rear heater
> control on the dash.  I believe that is the knob that is by itself to the
> left of the slide controls and looks like the one that controls the front
> fan.
>
> Turning mine seems to have no impact on the back heater.  I feel some heat
> there all the time but I thought perhaps there was a fan there.  What is
> the knob controlling if not a rear fan speed?  If it is used to control a
> fan under the seat then I suspect I've found another thing to repair.
>
> Eric Caron
> 85 Westfalia GL Auto
>
>