I am late to the party here, but I think from your original post you are mixing up the direction of flow, and that is causing confusion in the replies. The #8 line on your existing evap is not a return line, it is a supply line...this is the high pressure liquid input to the evap. The #10 is the vap...

"so I added some and will wait to see if it holds"

Hopefully what you added did not have sealer in it. Those fancy cans at the parts store with the short hose and low pressure gauge have sealer, and will gum up your system. And those gauges are notoriously inaccurate

I expect the sensor on top of the accumulator is the LPCO. I'd replace that, it most likely has a shrader underneath it so you don't lose charge when replacing it. You don't want to lose the action of the LPCO, since that protects you in case of a refrigerant leak. A system with insufficient refrige...

One thing that comes to mind is a faulty LPCO that lets it stay running, although that would not account for the comp running when not turned on, unless as Cusser mentioned

Make/model/year always helps.

"my system imediately pulls to the low side cut off and shuts down the compressor. "
From here it sounds low on refrigerant. It sounds like the LPCO is doing its job.

Have an AC shop test for leaks, evacuate, and recharge by weight

Cusser, you can get your 609 here: https://ww2.epatest.com/ The test is really not that hard, you already know at least 75% of the answers and further, you are a smart guy and it is open book. For a guy like you, it would prolly be a good idea. Might even consider getting your 608 in case you want t...

Cusser, our wonderfully devoted EPA forced eBay to ban R12 sale. You may still be able to find it on facebook marketplace. Eventually, tho, he will end up with 134. I would bite the bullet and do the conversion. You will have to adjust the POA valve, or get one from eBay that has already been adjust...

Indeed....

"I discovered that the pressure switch is not activating the High fan speed" This will definitely impair the system. Sounds like your flushing method was quite acceptable. When you say the refrigerant is 137a, do you mean to say 134a? "Now what intrigues me most is the compressor is c...

You may also have what we call re-heating. Your blend doors may be acting up and allowing heated air from the heater core to over mix into the cooled air. The hot air always wins.