I'm working on a stand up commercial freezer that has a adjustable manual valve on the suction line that you need a allen wrench to adjust. is this a capacity control valve? This is a R-12 system
Most likely a CPR valve to keep crankcase pressure down after unit comes out of defrost.Would only be a capacity(EPR) if you have multiple circuits.
This is most likely a crankcase pressure regulator as stated above.