Check Ken Wilford's site (Vanagain.com) for a very detailed how to.  Basically you have either a bent control cable or a bad valve.  The valve is located above the spare tire well.  Not sure how much trouble it is to replace the cable.  Being in Texas I just closed the valve manually.

Chuck
'85 Wolfsburg Westy - 'Roland the Road Buffalo'

> Date:    Mon, 23 Jul 2001 10:23:56 -0400
> From:    Wade Shen <swade@UMIACS.UMD.EDU>
> Subject: Endless Heat
>
> Hi all,
>
> It seems that my '85 westy is filled with hot air.  No matter what the
> temperature setting is, I get only hot air coming out the vents, altought it
> is hotter when the temp control lever is all the way to the hot side.  After
> screwing around with the temp control lever and the connection to the heater
> control cable, I'm beginning to suspect that it might be the heater valve.
> Can someone tell me where this thing is and how to access it?  This probably
> seems like a simple question, but Bentley HVAC chapter doesn't seem to
> detail this.
>
> thanks,
> wade