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?