For my two cents place gauge on suction side then after pumpdown and compressor shuts down kill power to compressor breakers fuse etc. then I front discharge valve on compressor and watch for a pressure increase if pressure rises your liguid line solenoid valve is leaking past .The reason I front seat the compressor discharge side is if valve plate or valves are leaking back from high side your suction pressure would increase found this out the hard way suspecting a bad valve also turned out valves on compressor was leaking .Be sure to leave power off until you backseat compressor discharge valve or you can damage the compressor .Hope this helps Jim
Pump the circuit down and close of the suction ball valve. Make sure the high pressure line to sorit is closed as well. Put your suction gauge on the circuit in question upstream of the suction ball valve. Turn of power to LL solenoid coil and open LL ball valve.
If the solenoid is leaking by you most likely will notice the outlet of the valve is cold and may actually see frost form as refrigerant is metering through it. You would also notice an increase in the suction pressure on your low side gauge.