Oil logging in subcooler

This is a new supermarket. Low temp recirc CO2 and 407A on the top cycle. We are finding that oil is logging in the heat exchanger. The service company goes out and drains about a half gallon of oil from the angle valve located at the bottom of the plate exchanger. Engineers are still trying to solve. We are using two exchangers and run both. We shut down one at midnite with an eev and an hour later shut the other down. Not sure if that has anything to do with it. I wouldnt think so. Any ideas? Thanks

Joe,
Probably need a bit more detail as to how system is piped up etc.
As the heading says subcooler?

Sounds like low load on the cascade interchanger presumably on the R-407 Side; so Oil is a misnomer? These envelope or gasketed plates or?

Hi Joe,
you need to keep the oil in the compressor circuit with improved oil separation.

Turns out electronic expansion valves were wrong size on subcooler.