You can't tell the amount of charge by reading the low side pressure. If you are not using the proper refrigerant the pressures will be different. Charge by weight only with proper refrigerant into an evacuated system that is clean and has the proper amount of oil or take it to a competent A/C shop, tell them what was done and let them finish it.

__________________
1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)