Date: Sun, 17 May 2015 03:15:00 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Fridge problem... which thing is malfunctioning?
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>Don't do that. Ever. You're rated for six degrees (maybe eight?)
>out of plumb in either direction, which is far more than most
>absorption fridges. Running it on a hill when you're driving is ok,
>but not stationary. And the damage is cumulative and can only be
>repaired by opening up the unit and rebuilding it. I'll explain in next email.
It's pretty simple. The cooling unit contains, all under pressure of
around 350 psi: hydrogen gas. Water. Water vapor. Ammonia
dissiolved in water, and ammonia dissolved in water vapor; both at
various strengths. Possibly some free ammonia, I forget. And
finally, some sodium chromate powder suspended in the liquid bits,
meant to protext against corrosion (and intentionally or not to show
when a system has leaked, as there will be a spray of the powder at the leak.
The heat source heats the boiler which contains strong ammonia water,
sending water vapor and ammonia up to the top of the system where it
begins to fall down through the various parts I won't talk about
this; many complex and fascinating things happen including ammonia
condensing to liquid at the right place to extract heat from the box
and various other interactions, all dirven by gravity, the internal
slopes of the cooling unit, and the varying densities of the
components and mixtures. Ultimately it all ends up down at the
bottom where it's fed back into the boiler, but during
operation there are distinct areas where one or another material or
phase predominates.
If you run the thing far enough off level that the cycle is
disrupted, the boiler will eventually boil dry and the heat sosurce
with nothing better to do will bake the sodium chromate powder onto
the boiler wall, insulating it. There's no non-invasive way to get
the caked material off, and as it grows thicker the fridge struggles.
The burping thing is simple and has been blow3n way out of proportion
by folklore. Dometic suggest that if the fridge has been out for
service and in unusual attitudes where the stuff in the cooling
unit may have ended up in odd places, just before you re-install it
turn it upside down a couple times so it all gets mixed
together. That will eliminate any possibility of it having to
struggle to get the cycle going again when it's lit. There's no such
thing as letting it soak upside down or whatever, you are just giving
it basically a shake.
Yrs,
d
Yrs,
d
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