The Shraeder valve isn't the problem with the leaking switch. The valve
is only there to let the trinary pressure switch be replaced without all
the freon leaking out. When the pressure switch is unscrewed the
shraeder valve closes to seal up the system. When the switch is being
screwed into place it opens the valve as it is tightened into place. So
in normal operation the valve is always open to allow the pressure
switch to read the freon pressure. It is called a Trinary pressure
switch because it has 3 pressure functions built into it. Tri = 3

Mark

John Rodgers wrote:
> 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
>