I agree that it is just 1 cooling unit circuit. The ammonia coolant that goes through the freezer cooling section also goes through the refrigerator cooling section. Two possible causes for your problem (besides the entire cooling unit being defective) are poor door gasket seals in the refrigerator (test by trying to pull a dollar bill through the closed door seals), or poor heat exchange on the refrigerator (lower set) heat exchange fins on the back of the refrigerator. You could have correct heat exchange draft across the freezer fins and bad draft across the refrigerator fins.
You might search the forum for previous threads using the word "refrigerator"