This guy has an inline heater valve that should work for you:

http://community-2.webtv.net/VanStuff/VanagonWestfalia/

On 4 Jun 2006 at 13:18, Mark Pry wrote:

> Help -- I'm in Arizona and I can't turn the heat off. No matter what I
> do with the controls, heat comes out of the dash vents and floor vents
> when those vents should just be blowing fresh/outside air. Right now
> my best option seems to be directing the fresh air (which is now
> heated all the time) to the dash vents and then closing those vents.
> But still hot air leaks in, especially on my feet -- not pleasant when
> it's 105 degrees outside and the AC system is hardly the best in the
> world (I have factory AC).
>
> My mechanic replaced the heater control valve, but the problem
> persists. He says this problem is common to Vanagons and that many
> owners here in the hot climes have solved the problem only by
> bypassing their front heaters altogether. But that's an inconvenient
> solution (I don't want to lose heated defrost, for one), and at any
> rate it doesn't ring quite true to me ... I've had the van for a year
> now and have used it quite a bit in hot weather with no problems
> whatsoever -- until last week, when the heat started coming out of the
> fresh air vents.
>
> This seems to me different than the hot foot syndrome, which as I
> understand it is caused by heat seeping through the floor from the
> coolant pipes on the underside of the van. My problem is that my
> heater is now on all the time.
>
> Any ideas what's going on? I've checked the archives and so far can't
> find what I need there.
>
> Mark Pry
> 1990 GL
>