It seems like a basic question, but in all the talk I do not see any procedures to charge a system with manifold gauges. Can you guys comment on this? I have a set of gauges with valves on the high and low side lines near the connectors that attach to the car. Additionally, the low side has a valve right at the gauge. The gauge actually turns to open and close this valve. There is also a valve on the supply line (yellow line) right at the can. What valves should be open/closed while adding R134a into the system? What valves should be open/closed when reading the pressure in the system?