Unloaders dont regulate oil they are a capacity control look up suction cut off unloader or www.xpedio.carrier/idc/groups/public/documents/... sounds like you have an oil return problem which someone misdiagnosed, so they kept adding more oil. at this point i would recommend that you take a class on compressors at your carrier dealer and recheck the design of your system (piping sizes, unit sizing and air side design
5f Carrier compressors they used oil pressure to load and unload the heads. On the O6's they used refrig. pressure to overcome spring pressure and would load and unload that way. A loaded head would work like a normal recip. a unloaded head would by pass the gas back into the crankcase through a check valve in the valve plate or a bypass internal in the head or external back into the crankcase.