It's best to run at about 1,500 RPM with doors and windows closed and a/c on full at max fan speed for five minutes. After five minutes, pressures should be stabilized. Under these conditions the pressure you gave would be a little light. You will probably have to experiment some, every system is different. Use a vent thermometer and try to get about fifty degrees or a little higher under the above conditions. Going down the road at highway speed before the cabin begins to cool, causing the system to cut back, should result in vent temp below 50.