The sensor is on the high side line someplace. AC Delco part number 1551343

Again, a Mitchell subscription can be a big help. You can screen shot the wiring diagrams & save them, that alone is worth the $20 charge

https://eautorepair.net/Marketing/Default.asp

No friction material. Metal on metal.

Be sure to set the gap correctly when you reassemble it.

The high side is a 3 wire pressure transducer that feeds high side pressure information to the PCM. The PCM makes the fan speed decision. It is not a simple switch, and is not adjustable. It is a 5 volt input, with a 1 to 4.5v output. The sensor could be bad, or the wiring to the sensor. The high si...

Many times someone has a vehicle for a few months, and has no history on it. Since you have owned it for a long time, you know that this is a new issue. You replaced the entire system - was there a reason to go after the Evaporator? Your radiator fans would be the logical place to start. I believe t...

The fans should change speed depending on cooling load. This is normally decided by refrigerant pressure & ambient temperature. A few questions: Have you owned this car since it was new? When was the last time you changed the cabin air filter? Are there some clicking or popping sounds from the d...

It depends on the overall condition of the compressor when it comes to the case O ring. If it has lived it's life in a wet corrosive environment like salted roads, it is probably a belly leaker. If it is an Arizona car it is less likely to have that issue. Here is the teardown for that job: https://...

Any positive displacement pump is variable output by changing the RPM The electrically commutated PMDC motors are fairly efficient over a broad speed range. So there is no need to use a variable displacement compressor with a variable speed motor. A little Sanden with a direct drive (no belt losses)...

Use a similar sized valve - forgot about the external equalization. Unless you live in some remote spot, there is an industrial hose shop somewhere nearby. The Aeroquip stuff works well, but you need to use the whole system - hose, fittings & tool Some odd MVAC fittings are not available from Ae...

If you had both service valves closed during testing, then yes the high side is too low for a good compressor.

Given that you have a POA valve, this is probably an A6 compressor?

Year / Make / Model would be a big help in helping you diagnose this system

I believe the 1979 Mark V still had a POA valve on the low side. The low side should remain steady, and around 30 psi. That heater valve was a great idea 40 years ago. They are subject to the ravages of age, and poorly maintained cooling systems. Since it is 105f here in Las Vegas right now I would ...