Early model 30 series had that valve manifold at the compressor. Every one I do A/C work on where I have the lines loose from the compressor, that valve goes bye bye and the later style lines go on. I stock the later lines on my service truck mainly just for that purpose. To answer the question about the position of the valves, turning them in will close off the system. Mid way will allow for flow through the manifold while allowing pressure to the service ports. When you remove the gauges, back the valves all the way out to allow for full flow through the manifold and block the pressure from getting to the service valves where there may be a possible leak. Good luck.