I'm new to the forum and really liking it so far but really need help or rather advice to help me find a leak on this rack. The rack i'm working on is a parallel refrigeration rack using R-404a gas and is being used for low temp cases. This rack has 12 circuits and handles coffin freezers, W.I.F's, and multi deck closed freezers. For the past month I have being trying to locate a leak on this rack. We are losing 100 lbs of refrigerant every 2 weeks. Now with that being said you would think the leak should be easy to find but unfortunately I can't seem to find it. I spoke with several tech support agents @ Hill-Pheonix and have no luck. So we are clear this rack has 4 compressors, 12 solenoid valve's, 12 EEPr's,12 suction and liquid ball valves, 28 evaporators and txv's. I do have & circuits that do run underground in 3 seperate chases. I have checked all evaporator coils, all TXV's, all solenoid valves, all schrader cores( I have found 6 cores leaking badly on liquid line and replaced cores with new), found discharge service valves gasket leaking on 2 compressors and replaced both, rack has a tube and shell heat reclaim coil and I have isolated it from high side of system and nitro test @ 300 psi and it held for 24 hrs with no pressure loss. I have closed suction ball valves and fed liquid into suction lines for each circuit 1 by 1 and allowed pressure to reach 135 psi and set to deforst and searched each circuit 1 by 1 with no success. The only thing I haven't done is isolate each circuit, pump down and recover residual to vacuum pump to 300 microns to see if circuit holds vacuum but I was hoping maybe there are some other ideas you all can share with me to see if I can locate and eliminate this leak. I have searched for this leak with a standard leak detector, ultra sonic leak detector, nitrogen, and soap bubbles. SOMEONE PLEASE HELP ME LOL..
Any advice will be more than appreciated. Thank you very much.