The suction pressure refers to the pressure of the referigerant being "sucked" back into the compressor. The suction pressure is a critical variable...
Inches of vacuum. Thirty inches of vacuum is generally considered a complete vacuum when evacuating a system before purging it with nitrogen gas to completely dry the system out before recharging it...
learn to read the chart for the type of freon you are running - a standard home unit will suck at 67 lbs and the high side will vary according to the outside ambient air temp - I get different...