Re: Heat in truck

[jlandry@domain.elided (John A. Landry)]

An example of "Dan Nees" <cookiedan@domain.elided>'s troubled thought patterns:

>I checked the heater valve and it operates fine. When I close the valve 
>when driving the heat does stop. The 'problem' is that the 71 is so air 
>tight that the heat doesn't seap out or blown out or something like 
>that. All the control levers work, I'm just want so regulatory tricks to 
>use on the heat.

Dan,

If you understand the way the heater control valve works, you'll also
understand why the heat output is so hard to regulate.  Here's the skinny...
The inside of the valve housing is more or less a straight tube.  The valve
"gate" part (inside when fully open) forms a straight flow through tube.  As
the valve gate closes, it's like sliding two circles sideways across each
other.  What difference does this make?  Well, it's sort of hard to explain in
text, but as you move the heater control lever say 1/2" from fully open, the
movement of two circles doesn't close off much total area of the circle.  So
there isn't much effect on the heat output.  But, as the two circles of the
valve gate further overlap, the open area shrinks in ever increasing amounts
for the same movement of the heater control lever.  Thus, as the open area of
the valve gets smaller, it takes ever increasingly smaller movements of the
heater control valve lever to keep from completely shutting off the heat.
Couple this phenomenon with a bit of slop in the heater lever control cable,
and you have some fiddling on your hands.  The key is to keep shutting down
the heat in *extremely* small movements of the heater control lever.  You can
just sit there and throw the lever back and forth... no good!

A helpful fix you might want to try...

On the original factory heater control valves, there was a small slit cut into
the face of the gate valve.  The aftermarket one I purchased didn't have this
feature.  The slit was only long enough so that when the valve was completely
closed, no coolant escaped through.  But, when the gate was partially closed,
the slit made control of the heat much easier.

You could take a jeweler's file and cut a slit in like the original.  If
you're interested in doing this I could draw you a picture explaining what I
mean and e-mail it to you.  I did this on my replacement valve and it really
helped the low heat output controllability.

Take care,

John

------------------------------------------------------------------------
jlandry@domain.elided             |
Conservative Libertarian        |  Scout(R) the America others pass by
Life Member of the NRA          | in the Scout Traveler escape-machine.
WA Arms Collectors              |
Commercial Helicopter - Inst.   | 1976 Scout II Traveler "Patriot" model 
http://www.halcyon.com/jlandry/ |     1977 Scout II Traveler (Parts)