Hi John, 
My brother is a certified air conditioning mechanic.  I will forward your message to him, as he will I'm sure know.  I know he has worked on Vanagons before.  

Julianna
1991 VW Vanagon Westfalia (Ophelia) 
1987 VW Vanagon Tintop (Armand)

> On Sep 30, 2016, at 1:38 PM, John Rodgers <jrodgers113@GMAIL.COM> wrote:
> 
> I have done some more thinking on this, and now have more questions.
> 
> When the trinary switch failed, the AC system was not running. In fact, it
> had never run while in my posession, even though I had serviced it to get
> the compressor to run . I had it flushed, then put on  a new receiver
> dryer, added a 134a conversion kit, pulled a vacuum check, and then put in
> PAG 46 (I think that is the number recommended, and one  can of
> refrigerant. The compressor should have turned om. It did not. I checked
> the clutch, and it did not engage. I jumpered it and it worked fine.  Also
> turned the compressor  by hand with clutch engaged. Compressor turned fine.
> I assume an electrical problem. And never turned the system on again. For
> whatever reason, the shrader valve under the trinary switch failed,
> allowing the refrigerant to blow out,  which in turn also blew out the
> switch. Replacing the shraeder valve with another supposed good one from a
> 134a converstion kit was not sufficient. It blew out as well, causing the
> loss of refrigerant again.
> 
> There was only the pressure of one can of refrigerant present, and the
> system had not yet been run. So this shraeder valve failure really puzzles
> me. As I see it, there was not enough pressure there to cause a failure, if
> the valve seals were good.
> 
> The fact of a failed trinary switch may have created the illusion of a
> failed shraeder valve. The switch could have failed pressing on the valve
> much like a thermostat will hot instead of cold. I am thinking of removing
> the trinary switch again, replacing the shraeder valve and just leaving the
> trinary switch off until it is recharged with one can of refrigerant. If it
> holds, then I will install my new switch, and see if that holds. I'll turn
> the system on, and  if  the compressor kicks on(it should - it did on my
> '88 model), then I will finish recharging the system.
> 
> I know a blockage somewhere could cause a problem, but the flush was done
> with receiver/drier removed, and the crud wash out of the hoses in all both
> directions intil it was clear.  The condenser section was done separately
> from the evaporator section. I was right there when this was done, so I'm
> fairly certain the system is clean.
> 
> In preparing to do this again, if anyone feels I've missed something, I
> would appreciate hearing about it.  Around here locally there's only one
> guy  to talk to about this and his is a system he built, so its very much
> not VW, and the  nearest shop is over in the big city.
> 
> Any comments would sure be appreciated.
> 
> Regards,
> 
> John