As you may have figure out by now. I am tearing up my AC system and don't know what I am doing. I have an a/c manifold gauge with a sight glass and can't figure out how this thing is going to work. once connected to the high and low side. Do I open both valves to let refrigerant through so I can see it in the sight glass? If that is the case, is it OK to let refrigerant bypass condenser, orifice tube and evaporator? I also suppose that if I can do that, the reading by the two gauges would be wrong in that moment. I suppose that to check the low side pressure, the high side valve needs to be closed and also to check the high side pressure the low side valve needs to be closed. I appreciate your knowledge, I can't find information on these small details.