read this first;
http://www.vanagon.com/info/articles/Refrigerator/Reefer_Madness.htm

Try removing the flute vent cover and using a strong
vacuum to suck any crud out of the two pipes.

  at worst case, pull the fridge and clean out the combustion
chamber...after 15-20 years all kinds of crud gets in there...

>Hey all (most wondrous oracle of VW knowledge and wisdom), I can't get
>my dometic fridge to run on propane. The electric system works fine, I
>have plenty of gas, I have spark I can see through the little sight
>glass.
>I notice there is a kind of pin in the front lower left of the fridge
>with a little chain on it. Am I supposed to do something with this?
>The fridge instructions don't say anything.
>
>Nathaniel