96 A/C OIL QUESTION

HERES A GOOD ONE! I'LL TELL MY WHOLE ORDEAL.
I CHECK FREON IN MY 96 CHEROKEE SPORT AND P.S.I. WAS LOW (20) SO I BOUGHT
A CAN OF FREON WITH 2 OZ OF OIL(PAG), LEAK DECTECTOR,SEALER,ETC.
I ADD THAT CAN AND IT WAS STILL LOW. I ADDED ANOTHER CAN OF THE SAME STUFF
THEN I GOT PROBLEM: P.S.I WAS WAY HIGH AND COMPRESSOR WOULD ONLY TURN ON FOR
2 SECONDS THEN OFF FOR A BIT REPEATLY AND AIR WAS NOT COOL.
HERES WHAT I DID(DON'T TELL THE LAW; I HATED DOING THIS)TO FIX MY PROBLEM
I WAIT FOR THE COMPRESSOR TO ENGAGE AND OPENED THE ZERK FITTING UNTIL
OIL CAME OUT AND IT LOOK LIKE THE OIL AND SEALER, ETC I ADDED CAME OUT 4-6oz
AND THE COMPRESSOR STAYS ON AND I HAVE 30 PSI @ 75-80 DEGRESS HEAT AND COOL AIR.
I GUESS MY QUESTION IS HOW MUCH OIL IS NEEDED IN THE A/C SYSTEM? SHOULD I ADD SOME
( ABOUT 2oz) OIL? ANY HELP WILL BE GREATLY APPRECIATED!