Just bought the truck and compressor was constantly cycling. So discharged the system put back 20ozs so far. Ac compressor doesn't cycle on at all at this point so I'm thinking I have a bigger issue somewhere. What could it be

 

You have two pressure switches on the the ac lines, One high and one low. If the low pressure switch is not being triggered(due to low refrigerant pressure) the compressor will not come on. High side cuts off the compressor if pressure goes over the limit. You discharged the system but did you evacuate it? Also did you use pro gauges or that trigger bottle ac crap. Forget the amount the ac system takes but it's more than two of the small bottlers of refrigerant.