[Bigdav160]

I don't think many people are happy with the POA eliminator pictured. It turns your system into a cycling system that is normally used with a orifice tube.

Originally, and mostly likely still do, you have an expansion valve as the metering device. It's used with a continuously running compressor.

The POA helped control the pressure in the evaporator core. More modern A/C systems might use an expansion valve without a POA. By adjusting the expansion valve you might be able to get decent performance without the POA. The switch above would then become a protection device

edit to answer your questions.
I do not believe you can buy a "new" POA
The wire on the switch goes in series with the green wire going to your compressor
Google a 134a pressure/temp chart. While running low side pressure should be 35-40 psi.