Date: Fri, 4 Jun 2004 13:29:38 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: permanent fridge damage
In-Reply-To: <5.2.0.9.2.20040604121340.0393be68@mail-hub.optonline.net>
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At 12:21 6/4/2004, Tim Demarest wrote:
>According to my source, who got it from an RV fridge repair specialist,
>off-angle operation causes the ammonia (which acts as a refrigerant in
>these beasts) to condense in the wrong parts of the system. Over time,
>this can cause deposits to precipitate out of the ammonia in various nooks
>and crannies of the system.
Your informant got two things slightly mixed together:
First, it's a gravity system that depends on a rather tricky combination of
vapors and liquids -- water, ammonia and hydrogen in various combinations
-- flowing down hill (there's a good explanation with an excellent diagram
at www.rvmobile.com ). So when you tip it the cycle doesn't work as well,
and if it's tipped too much things can indeed pool where they
shouldn't. The damaging result though is that the boiler boils dry which
causes the anticorrosive stuff to build up a hard burned cake on the side
of the boiler. This impairs the process permanently and if it happens too
much kills it. Either way it can only be repaired by opening the cooling
unit, cleaning out the crud and recharging it with new working materials at
350 psi or so. I believe the operation spec for the Dometic RM182B is +/-
8 degrees, which is more than most (typically +/- 3 degrees one axis, +/-
six degrees the other axis I think).
When you're driving the cycle doesn't work as well because of random
accelerations as well as hills and such, but because of the random bumps
you don't normally have the danger of damaging the unit.
>The recommended repair was to pull the fridge, and leave it turned upside
>down for a few days, giving it the occasional bump and shake (not enough
>to do damage, but enough to stir the inner fluids). This should allow
>liquid refrigerant to get into the upper reaches of the system and
>dissolve these deposits back into solution, resulting in improved cooling
>once the fridge is turned upright and re-installed.
Second, as I said you can't repair that kind of damage short of rebuilding
the cooling unit. However, Dometic recommend that after servicing a
fridge, *in order to help it establish cooling as promptly as possible* you
should tip the unit briefly on its side -- all four sides if I recall
correctly. This simply makes the working fluid reasonably homogenous to
begin with so that everyone "starts square." It will soon establish itself
in the right concentrations and places when heat is applied. It's the last
30 seconds of this process that matter; you can do anything you want for
the previous three weeks without measurable effect.
david
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
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