Re: [VAC] Ammonia cycle refrigerators.

[Chris Bryant <bryantrv@xxxxxxxxxx>]

	I do a *lot* of work on ammonia refrigerators- at one point I considered
rebuilding them (seemed to be way too much hasle).This week I have three
that I am installing Midwest rebuilt cooling units in.

	The older units (pre 1979, or there abouts) applied heat directly to the
boiler tube- a 1/8" tube. Since the burner flue and electric heating
element(s) were right against the tube, and since the refrigerant (ammonia)
is circulated purely by gravity, if the refrigerator was operated off
level, the ammonia solution could "pool" in the upper tubes, starving the
boiler tube for liquid. This would cause it to overheat, and cause the
anti-corrosive agent to crytalize, clogging the boiler tube. The fix for
this was to cut the tube out, and either clean it, or replace it.
	Most of the older models would fail in this manner, rather than leaking.

	The newwer models have the boiler tube wraped inside another tube, with
ammonia in it- they are much less likely to overheat like this.. but...

	When the manufacturers (mostly Dometic) got to this stage, they started
x-raying (they didn't use x-rays, but something similar) the cooling units
while they were operating. They used this info to remove any un needed
material (they made the tubing thinner). This has led to the way most
newwer units fail, the dreaded ammonia smell- a leak.

	This is getting kind of long winded, but the upshot is that any older
refrigerator is a good candidate for rebuilding- except for the issue of
parts availability (I tried to find a ceramic burner for a late '50's/early
'60's Dometic- no luck).

	This, of course, does not take into account weight (new refrigerators
weigh 1/2-2/3 what an old one weighs) or convenience (with everything
working- it is pretty nice to just push a button, and have it work).

	Sorry this was so long..

________
	
	Chris Bryant
	Bryant RV Services
	DeLand, Florida
	mailto:bryantrv@totcon.com