I have recently replaced a 5h80 open drive compressor, tube in shell evap, and expansion valves on a industrial chiller. a 500 micron vacuum was pulled (took four days) h-48 drier cores (2) were changed and system is charged with r-507. system brings glycol down to 0deg. set point, but my head pressure is always well above ambient + 30deg. my sub cooling (before sub cooler) also goes up/down with outdoor temp. i think there may be non-condensables as there does not seam to be a lot of heat rejection at the condenser. i also seam to be pumping about 1/3 of the oil thu the system all the time. my compressor holds just under 6gallons and i had to put 9 gallons in to keep the level at 1/2 sight glass. my superheat stabilizes at 6deg after about 10 min running from a restart, and as long as the ambient stays below 80 deg my head pressure is below the 400# safety lockout. all my condenser fans are running and the coil is very clean, even sparying water on it does not seam to do any good. i have changed the oil/driers once since putting this back n service but that did not seam to help either. what should i look for next?