Another A/C question

When charging A/C is it necessary to open both the service valves a little or just the suction?

Depends on what kind of service kit you are using, if it's just a can and single hose recharge just hook the can to the low pressure side, engine running, air on high fan on high and open the valve on the can. I turn the can upside down, it empties faster as a liquid.
If it's the 3 hose setup then follow those directions or the ones in FSM, they have a step-by-step procedure.