i ve heard you can change a a/c unit into a air compressor for bags but no one seems to know how any tips  

yes you can. i had one rigged for onboard air on a wrecker i used to have. adapt your airline to the high pressure side, install a guage and pressure relief valve somewhere in line or on your air storage tank, run the intake line (low pressure side) to your air cleaner so it gets filtered air. you can rig an air tool oiler in line on the intake side or simply put some air tool oil into intake line once a month or so.  

Hey there scavengerdog I've been wondering the same too, only i saw it done in a truck magazine. So how do you wire the compressor to turn the clutch off once the tank has reached pressure.