We picked up new account today its a food processing plant 8 copeland compressors mt and lt rack common discharge seperate suctions accumalator on lt compressors. Mt suction running 42# lt at 8# rmcc controlling rack and temps eprs on all evaps liquid line solenoids for defrost. All oil failures are wired properly and tested. Temp sensors on all suction trunks to monitor compressor superheat. Compressors breaking about every three months one after the other. R404 poe the plant used to run on r12 mineral oil one on ones. Rack was installed with air cooled condenser. Vf d head at 170. Any ideas as to whats hapening?