Date: Thu, 21 Aug 1997 17:09:16 -0700
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Richard Angelini <richard@BALLY.COM>
Subject: How Propane Fridge works
Hello fellow Dometic fridge owners,
Here are some hopefully helpful notes on the theory of propane operation
in a Dometic Fridge. Understanding how it works helps get the sucker
lit. So here goes...
Step 1:
Ok so first you turn on the master gas valve on the propane tank. Gas now
flows to the fridge. The gas stops at the fridge gas valve. Its positioned
like this (-) when OFF.
Step 2:
Now you turn the fridge gas valve to the ON position (|) . Gas now flows past
the value thru the thermostat and stops. It stops at the ignition button
because there is no flame in the fridge combustion chamber. This is a safty
feature, gas must be burning in the combustion chamber for the gas to flow.
A thermo-couple in the combustion chamber senses the flame and electrically
tells the ignition button when its safe to pass gas (no pun intended I think).
Ok, so you ask then how does gas ever flow then? Step 4 reveals that little
secret, read on...
Step 3:
Now we need oxygen to mix with gas so it can burn, so you stroke the air
pump to get some oxygen down into the combustion chamber. Remember that chamber
is sealed air-tight and its only inlet is 2 /12 feet up a small metal pipe to
the van side vent (the air-tight seal is so carbon monoxide goes out the metal
exhaust tube, not into the van interior). The higher you go in altitude, the
more you have to pump to get oxygen down into the chamber (since the air is
thinner).
Step 4:
Now all is ready, we have oxygen and almost have gas. Here is where the
ignition button comes in. You now press the ignition (or safty override)
button. It physically opens allowing gas to flow even though there is no
flame into the combustion chamber.
Step 5:
Pressing in on the air pump causes a spark in the combustion chamber. If the
gas lights you still have to hold in the ignition (safty override) button
for a few seconds. This gives the thermo-couple time to sense the flame and
tell the ignition (safty override) button its OK to pass gas (yup its that
pun again).
Step 6: If the gas did not ignite you probably had too little oxygen. This can
happen if you did not pump enough, or you held down the ignition (safty
override) button too long. Holding the safty button in too long lets the gas
push out the oxygen, or if the too rich gas mix is just right cause a small
POP like explosion. In which case you have just pushed out all the oxygen you
pumped in. So you go back to step 3 and try again.
One miscelanous note. That little metal tube at the bottom front of the fridge
it there to let you drain out moisture out of the combustion chamber. Burning
propane in a cold metal box (the combustion chamber) can cause some water to
form. The tube lets you drain it out. And since its water the tube gets rusted
over time.
Another miscelanous note. The propane feature is NOT maintenance free. Over
time the combustion chamber and intake/exhaust tubes will need cleaning, the
gas orifice in the chamber will need to be cleaned or replaced and the sight
glass will need to be cleaned. Sooooo, sooner or later you will have to pull
the fridge and do this.
I hope this helps you understand lighting the propane fridge. Once I understood
how mine operated its worked perfectly.
Richard Angelini - 85 Westy