I sure have struggled with this system.

Just above the high pressure service port there is a port for a shraeder
valve. Scriwed onto that port is an electrical deviced called a "trinary
switch". I have no I dea what it does or how it works. Seen from the
shrader valve end there is a pin that obviously works asinst the stem in
the shraeder valve. It is electric -4 wires - but what does it do? How does
it work? What does it regulate?

Driving down thevroad I heard a loud pop, then a whistling like air from a
tire. I stopped to investigate and foundcthe bach of the trinary  switch
blown off, suggesting that the shraeder valve underneath had failed. I
removed the switch, replace the shraeder valve, and reinstalled it,
thinking I MIGHT just put the rubber seal back in place, and all would be
fine. NOT!!! The minute I added a can of refrigerant and presurerized the
system, the seal popped and I was back to square 1, suggesting the shraeder
valve failed again.

Not knowing the relationship of that trinary switch to the shraeder vslve,
I'm reluctandcto trymit again until I learn more about it.

Can anyone enlighten me?

Thanks.

John