My 85 Vanagon had an automatic fill valve which caused nothing but trouble at the fill stations.
Some even refused their service as it was not worth it to spend 15 minutes and only put in 1/2 a gallon!

Here is how I fixed it:

Emptied tank by lighting burners. (outside with windows open)
Unscrewed fill valve and took it to a local propane parts store and bought a plain manual fill valve for about $25.
Screwed new valve back in (used a bit of Teflon on the threads).  
Went to a propane place and filled tank with no problem.  

No problems since (about 10 years now).

This was a long time ago, I forgot all the details but use your common sense.  Make sure the bleed valve 
is still there.

Alfred
85 Vanagon

PS:  Donated the automatic valve to the brass recycling pile at the propane parts store.

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