Oil return issue

Hi Guys

I am having an issue with oil not returning to the compressor sump (Bock Hg34e/315-4s), I have since replaced the oil separator and oil pump. Upon startup, the oil gradually leaves the sump, and returns only once the compressor has been switched off. This is an existing system that has been running fine for a number of years. It is a R22 medium temp application ( Drop temp coils, room temp 7 degrees Celcius.)

Much appreciated

Welcome to the forum misterwerns

Is your suction superheat ok? Discharge running too hot? piston rings shot? R22 is generally a good oil return gas, what has changed that led you to replacing the components?