Working on a McQuay centrifugal M# CE063JAP18RDU STYLE# 068368201F ... The oil filter housing seems to be molded into the compressor shell Ther are only two lines leading into the housing ...I close both ,also close both the lines leading from the oil tank and cooler. loosen the oil shell cover and as expected the oil still under pressure foams out. The limited info I can find says the chiller contains a check valve internal to the filter and it should stop the oil foaming and eventually the pressure wil decrease to the point where I can remove the filter. My problem the oil foams out for over ten min.. Anyone ever have the "check valve" fail... Is this normal and is that filter housing open to the compressor and or impeller??