hello , and thanks , the oil will return up the suction , then into comp crankcase , they are scroll comps, so they will need to discharge that oil , and i find with scrolls they dont discharge that much unless comp is really high with oil , then they have no choice , like i say i did try to increase back pressure right up turning off the pack , , but still no return , i also put several case on defrost to allow the extra load on start up ,think maybe i could let jus one comp run alone to see if this drags it back , of course if here is oil trapped to drag back , because this i dont know ,