AC clutch not cycling

so A/C was not as cold as should be. used AC pro can. A/C was on bit low side. filled up system a bit and everything seemed to work fine. drove truck the next day and only blowing warm air. A/C clutch engaging for a second or two then shutting off. put A/C pro gauge back on to check pressure. when clutch engages the pressure drops then shoots back up into yellow zone when clutch disengages. If the system is overcharged, how do i properly depressurize it?