The system is designed so there is always air flowing through the heater boxes. Even when the heat is off. That is why the flaps have opening on top. Without the air the sheet metal outer boxes burn up and the exchanger core can crack.

Dennis

Sent from my Windows Phone

-----Original Message-----
From: Mark L. Hineline
Sent: Monday, December 27, 2010 2:54 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Physics phun

> Okay, I have one good heater cable and one good flapper valve, both on
> the right side of my 82 aircooled van. I'll be scrubbing the boneyards
> for the missing parts, but in the meantime I'll be wanting some heat.
> 
> As luck would have it, I live in So. Cal., so I don't need a lot of
> heat, but I need some to the defroster and some just because I'm
> getting old.
> 
> Somehow I have to cap off the heater ducting in front of where the
> left bellows would attach because I haven't got a flapper over there.
> That's trivial.
> 
> The non-trivial part of this work around is that I need to block some
> of the air going from the alternator-mounted fan over to the left heat
> exchanger.
> 
> - I don't want to block all of it, because that would lower the
> effectiveness of the working exchanger, on the right, because all the
> air from the fan would be passing over it.
> 
> - I don't want to spill all the air, because that would lower the flow
> through the right half of the system too much.
> 
> So: how much should I block? And any good ideas about how to do it?
> some kind of a baffle?
> 
> Thanks,
> 
> Mark