A refrigeration unit and diagnostic method therefore are provided. The refrigeration unit includes: a housing with an insulated cavity for storing food and beverages; a vapor cycle system operative to cool the food and beverages in the insulated cavity; a plurality of sensors in communication with the vapor cycle system and outputting data relative to the vapor cycle system; and a controller that, according to the data from the plurality of sensors, determines an occurrence of an event. Wherein the controller logs the data from the plurality of sensors to a data structure according to a first data-logging mode, and logs the data to the data structure according to a second data-logging mode upon occurrence of the event. In one embodiment the refrigeration unit may be a refrigeration line replaceable unit (LRU) configured for an aircraft galley.