Date: Mon, 26 Apr 1999 12:23:28 -0400
Reply-To: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject: why pre-heat, explained was: Refrigerator Problems
The reason that "pre-heating" the refrigerator on 120 or 12v helps get the
propane cycle working is pretty simple. The stainless-steel exhaust tube
for the refrigerator warms up...
Okay, now you are going, "Huh?"
Some will tell you that you run the electric to "pre-heat the ammonia", or
some other mystical part or fluid inside the refrigerator. Poppycock.
The propane burner assembly doesn't care what temperature the ammonia is.
All it cares about is getting the right mixture of propane and air, and
being able to exhaust its waste products efficiently to the outside the
van. That's all that flame wants out of life. When the exhaust pipe is
cool, it can't exhaust very well, and it chokes.
Think about the density of air for a moment. Hot air rises, right? Of
course it does.
The exhaust from the propane cycle has a long distance to travel, and very
little "motivating it"; only the difference in its density to get it there.
The meager exhaust from the tiny little propane flame that you light in
the bottom of your fridge has a run of about two and a half feet of
corrugated stainless steel exhaust before it makes its way to the outside.
When that stainless steel tube is cool, the warm exhaust quickly cools,
thus becoming denser, and it loses velocity. Soon the flame smothers itself
in exhaust. Complicating matters when the pipe is cool, moisture present
in the exhaust may condense in the cool pipe, and run down into the burner
area, extinguishing the flame.
By running the refrigerator either on 12 volts or 120 volts, the entire
rear area of the refrigerator warms up, thus warming the stainless steel
exhaust pipe, making the propane cycle much more likely to work from the
get go.
Instead of running it on electric, I find that by gently pumping the air
pump, after the flame is lit one can effectively drive the warm exhaust up
the cool exhaust pipe, thus eliminating the need for pre-heating the
refrigerator.
The first few times that you try this, (pumping air into be burning chamber
after the flame is let), you may want a try it late in the evening when you
can watch the flame through the flame window. At least on ours, the
additional air will not blow out the flame, however you can tell when the
flame is beginning to smother, and pump in additional air that point or
re-light while the burner is still hot.
Party on,
G. Matthew Bulley
Bulley-Hewlett & Associates
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree
-----Original Message-----
From: Bob Stratton [SMTP:rslist@SDII.COM]
Sent: Monday, April 26, 1999 10:39 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Refrigerator Problems
At 08:39 AM 1999-04-25 -0700, Mike Finkbiner wrote:
>
>It cools on 110v and 12v, I can see a nice fat spark through the sight
>glass, but there has never been any flame. I pulled the outer vent
>cap off and vacuumed it out to clean up any spiders, etc. (After all,
>who knows what could have moved in while it was in North Carolina)
>After that I blew compressed air into the drain plug on the front to
>see if that would clear out blockages.
If you've already tried this, then ignore me, but if it seems to run on 12V
and 110V and the problem is that it just won't light, you can try this
technique.
The guys (J&R VW) I bought my Syncro from told me this, and it works like a
charm.
Run your refrigerator for about 45minutes on 12V. Driving or stopped,
doesn't seem to matter, though I'd probably avoid parking on big hills,
since it really needs a level surface to get going well.
After about 45 mins on 12V, try to start it with propane. Mine usually
lights up within 3 tries if I ran it on battery first. I have no idea why
this should work, as I can't see the 12V heating element being hot enough
to cause ignition, but it does help.
--Bob, KE4GDC
89 Westy Syncro GL
