What's up with the service valve on the low side of the monster Trane 16X, Mfg 9/2010?

I walked up to one today that would not start despite high and low voltage. Chased the control voltage past the delay and up to the small apartment that is the coil and quickly decided it has to be a LP or LOC switch. Hook up and go to open the valves and there is this odd rectangular deal on the low side with stops on it - like you can only turn it a quater or a half.

How does this valve work? Quarter or half turn down to open to gauges? What if you have to pump it down or isolate the condenser?

I might end up going back as there was oil all over the suction line at the evaporator coil. But the client is understandably going after the installing contractor first. It was only installed about 18 months ago.

Even though there is literally nothing left to recover, how do you close these Trane low side valves to isolate, leak check, repair, pressure test etc?

The high side valve appeared to be a regular service valve.

Appreciate any help as always,