Not being a "fridgie" all I can say is if the cascade system was designed correctly it is important that all components in both the circuits are working correctly and efficiently otherwise problems will occur.
Is there a problem with the unit, what temperatures are you dealing with, e.g. -700C, are your condensers water or air cooled, are your condensers fouled, what refrigerant are you using, have you checked your suction and discharge pressures on both units........................more information please.
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TO BE. or NOT TO BE. That is the question!! The Bard