I have an ammonia chiller using a compound mycom. When the unit goes down we have an oil loss issue. We have replaced the suction check valve and had a mechanic adjust the flow of oil through the vivkers valve. Now when the operators go to startup they have to turn on the oil pump to unload the 2nd stage. Doing this pumps the oil from the separator into the compressor, suction and inter stage piping. The only way we can get the oil back is to create a pressure differance by depressuring the oil separator and most of the oil returns but not all. This is becoming quite a problem and I am out of ideas.