Well I ended up removing the shrader valve from the suction port and pressurizing the system with compressed air. There was a loud and obvious leak at the high pressure switch that screws into the receiver/dryer. I picked a new switch up from a local AC shop. I also added some conversion oil and recharged the system with R-134. (I'm cheap) The system seems to be working OK, but not as well as with R-12. This is generally true with any R-134 conversion though. Hope my luck lasts!