An auxiliary thermosiphon has an auxiliary refrigerant conduit with an auxiliary evaporation segment in thermally conductive connection to an interior wall of the freezer. The auxiliary refrigerant conduit contains an auxiliary refrigerant that is isolated from the primary refrigerant of the primary cooling apparatus. The auxiliary refrigerant conduit also extends upward to an auxiliary condensation segment of the auxiliary refrigerant conduit at an elevation above the auxiliary evaporation segment. A thermal bridge is in physical thermal contact with the auxiliary condensation segment and in physical thermal contact with a portion of a primary evaporation segment of the primary refrigeration apparatus. Heat is transported through the thermal bridge from the auxiliary thermosiphon to the primary refrigerant conduit and consequently to the primary refrigeration apparatus for removal from the freezer.