Hi I have a rack of three bitzer semi hermetic compressors running one freezer room and three poolrooms. The problem I have is the units are tripping out on mechanical oil safety device. The oil levels in the compressors are controlled by trax oil controller. The system is on R404a and is 18 years old.
- Oil pressure across the three compressors is good at positive oil pressure of 35 to 40 psi.

Initially one of the trax oil level controllers would still fill with oil even when sensing full, this has been replaced, and 10 lt of oil has been put into system. Yet again the compressors are tripping on oil safety and the oil separator is showing no oil.
The oil separator does seem to work , as when the outlet of the oil sep is shut off it does fill, when you pump down we seem to get oil coming back to the compressors.
The weird part is on the receiver sight glass you can see about 1cm layer of oil ontop of the refrigerant. And also when the system is not asking cooling and the compressors are idle the refrigerant level in the receiver drops away, even when you pump down the receiver the level in the receiver drops away???? and conversely once the unit starts up the receiver fills up
Please help me find my oil