The pressure I quoted was in metric (mm Hg). If it is a liter of R134, then roughly, it should be about 33 ounces.

If you meant 30 mm Hg (not psi) on the low side with the engine running and AC on, you may be a little low on refrigerant. You still need to check the high side also to see if you are getting low pressure. Otherwise, you may overcharge the system, if you decide to add more r134.

John