[VAC] More old dometic (long)

[JIXIX@xxxxxxx]

Just got around to looking at the old Dometic (orig. in '66 Safari) this 
year...before our cross country trip (so will be off-list soon for awhile).  
Remembered better what I did several years ago to spruce up the propane 
running.  Others may not be the same in design..and don't do this unless you 
know what you're doing..but here goes.

There's a small hex nut that holds the burner unit clamped on a steel 
bracket, positioning it up near the steel tube where the hot air goes up.  
This tube is about an inch in diameter, and there's about a quarter inch 
space between the top of the burner, where you can see the flame when it's 
on.  The burner looks like a tiny bunsen burner, like you had in chem lab in 
high school.  It has a tube with a wire mesh on top, and a couple of air 
holes near the bottom, with a knurled ring that can be adjusted to set the 
amount of air being sucked into the gas stream.

By loosening the hex nut, the burner can be let down (the gas supply tube 
flexes to allow this) off the bracket (had to coerce it with a big screw 
driver, since the slot that fits around the bracket was tight).  Once the 
burner is down, you can carefully unscrew the whole burner tube from the base 
(NOT using the knurled ring...that would just disturb the air setting).  Here 
is where you may find simple improvement for your fridge.  There's a small 
depression where the burner tube was screwed in, with a tiny hole in the 
center where the gas comes in.  DON'T do anything harsh that would mess up 
this hole...it's machined to close tolerances to properly regulate the gas.  
But you may find a little pile of rust in the depression!  This is rust that 
has fallen down from inside the burner tube, and made it through the burner 
screen.  It will interfere with proper flow of the gas and mixing with the 
air.  This won't make much of a difference to the flame...just enough to make 
it not-quite-as-hot as it ought to be.  You can blow this stuff out of the 
depression with compressed air, or just blow through a straw.

Now use one of those automotive mirrors-on-a-stalk and a flashlight to look 
up the burner tube.  It'll be open a ways, and then there are baffles 
designed to improve the heat transfer from the gases to the fridge 
mechanisms.  What I did before was to poke up here with a bottle brush to 
loosen any more rust that might fall down, and then blow a little air up 
there to clean it out.  Of course, cover the burner unit while doing this. 

With the burner tube out, it is possible to adjust the air to the flame with 
the knurled ring, although this shouldn't be needed.  As mentioned in a 
previous post, the manual says the flame should make a buzzing sound (and 
appear like a little blue crown).  More air coming in makes the buzzing more, 
and I believe makes the flame a little hotter.  But you don't want so much 
air that any part of the flame crown appears to lift off the top of the 
burner when the tube is screwed back into the depression, and the flame is 
lit.

When clamping the burner back on the bracket, I believe the correct 
adjustment is so that you can just see the whole flame between the burner top 
and the bottom of the flue tube.

Of course, none of this will do any good if your fridge doesn't work on the 
AC.  That's the first thing to check.  If the AC will run it fine, then it 
may be worth checking for rust as described.  And, as others have said, the 
propane will not cool as fast as the AC.  Since you can't run ammonia 
refrigerators while in motion, my solution for the fridge while not roosting 
for awhile is that I added a plastic container next to the freezer 
compartment that sits on a rack.  (removed the top rack to do this).  It is 
big enough to hold a bag and a half of ice.  I added a tubing barb at the 
bottom, drilled a hole through the bottom of the fridge, and ran a small 
plastic drain tube out the bottom of the trailer.  The tube can be clamped 
and drained at appropriate times.  This turns the fridge into an ice box when 
not sitting in one place long enough to make the propane method worthwhile, 
and is very easy to fill with ice.

One more thing...don't forget there is a thermostat knob for the gas, behind 
the panel where you push the button to light the unit (if it's like mine).  
Turn this all the way up to start with.  It does affect the size of the 
burner flame...with an old fridge, I think it needs all the flame it can get 
to start cooling initially.

John
jixix@aol.com