Hello and welcome to Just Answer!
All you need to do is remove the a/c clutch relay from the fuse relay box in the engine compartment and jump terminal 30 to 87 and that will engage the clutch while you charge the system.
Click this link and download the diagram. http://senduit.com/066e3b
I hope this helps, let me know!
It is very hard to properly charge an automotive a/c system to the correct amount by just using gauge pressures. It all depends on ambient temperature and humidity. Refrigerant is pressure temp related, so the ambient temp has an effect on the pressure readings.
If you had a scale you could measure the amount you are putting into the system, the charge amount for front a/c only is 1.50 lbs and the charge amount for front and rear a/c is 2.38 lbs.
If you have no way to measure the amount your are putting in, it is very hard to know when you have charged it with the proper amount.
Click here to view a chart for different ambient temperatures and pressures.
Find your outside temp and compare it to the other readings.
I hope this helps you, let me know!