A/C Help

[scoobysteven]

I have an Infinity G20, 2002, P11. The refrigerant is just a little low, no major leak. I bought a can of refrigerant with valve indicating the normal operating pressure for the system. The can has instruction that are incomplete, and every website I've checked leaves out 1 MAJOR detail regarding the normal system operating pressure. Does the normal operating pressure apply to the vehicle at idle with the compressor engaged, or disengaged? This is a huge detail not mentioned in the instructions. The pressure difference is significant, like 20psi. So does the normal pressure operating range apply to car at idle with compressor engaged or without? Please help me understand.