I wrote to the list about this problem a while ago with the answer being the
control valve being warped and needing replacement.  That may not be the
issue, and my mechanic sez that what I say is impossible to happen, but here
goes:

Engine under normal temp,  using the fan I can get heat or "flush" the heat
out and get cool air with van not moving and moving the temp lever - just
like normal.  Same with driving.  I might note hot-ness factor is not that
hot, but then I have a Subaru conversion which may be contributing to that.

If the engine gets hot where the external fan goes on, I can still
manipulate the heat lever and control heat or outside air when the vehicle
IS NOT MOVING and only the fan is pushing the air, and the air is VERY hot -
all to be expected.

However, this is not the case when the vehicle is moving pushing air thru
the vent when "overheated" or hotter than norm.  While I can control the
temp sitting still, I cannot control the temp when driving - it is hot air
NO MATTER what the temp lever says, and it is HOT.  ONLY when the temp
returns to normal does the hot air stop and "fresh" / cool air once again
enters the cabin WHEN THE LEVER IS ON BLUE/FRESH!!!!!  This portion is
illogical.

If the valve were faulty, I would have the control problem no matter what.
And in a VW manual the pic only shows 1 valve control to the heater exchange
box.

Any ideas - have any of you experienced the same???  I seriously doubt this
issue is due to my Subaru conversion as that does not touch the
heating/venting system nor really change the coolant system save for the
interface with the engine.

Thanks!!

Joe Gawzner
90 Syncro Westy Subaru Conversion