The delivery/return air differential will, in most cases, narrow as the continuous circulation of air, being cooler than the cargo, brings the cargo temperature down towards the desired level. Any rise in return air temperature will be arrested as the refrigeration unit begins to run in standard operational mode.
When the stuffing temperature is higher than the stipulated carriage temperature, the refrigeration unit will cool down the surface layer of the cargo relatively quickly (within days). However, the center of the stow will not reach the desired temperature for a considerable period.

The temperature of a cargo stuffed into a refrigerated container should not, in general, deviate by more than 3 degrees C (5 degrees F) from the named carriage temperature. Chilled cargo (excluding bananas) should not deviate by more than 0.4 degrees C (1 degree F). This does not mean that even these differences should be encouraged; the objective is to receive and deliver the cargo at the carriage temperature.

Over-Tempreture Reefer Acceptance Guidelines

a) Temperature-controlled loads are considered “Over-Temperature” (“Hot Loads”) if they have varied from the maximum acceptance temperature set by the Charterers. However, use the available historical data, especially return and supply air temperature, relative to specific load to determine that the temperature is falling towards setpoint temperatures.

b) Loaded containers varying more than the above-outlined temperatures should not be received at a terminal for loading to a vessel without prior approval from the Container Operator.

c) If onboard a vessel, a unit is found to be "over-temperature," the container operator should be notified immediately using Reefer Container Trouble Report. Where instructed by the Charterers, the vessel's crew shall take action to correct the temperature of the unit by returning it to the proper set temperature.

Reefer Spare Parts

a) Each ship shall carry a designated pool of spare parts if provided by the charterers.

b) The container operator shall be responsible for supplying an initial set of any additional specific parts they require to be added to the vessel spare parts pool.

c) If a container operator introduces a new or different temperature control unit model, he is responsible for providing the initial set of any additional spare parts specific to the unit required for the vessel spare parts pool.

d) If a container operator phases out of a temperature-controlled unit he shall be responsible for collecting or requesting disposal of the relevant parts from the vessel's spare parts pool.

e) The Container Operator shall supply refrigerant gas and oil. f) The vessel shall be responsible for the onboard spare parts' inventory recording and is responsible for notifying the container operator to replace the spare parts consumed.

g) The Container Operator (or B/L carrier) shall replace all parts used from the vessel's pool for repair to their specific unit in the form of new parts or monetary reimbursement. The vessel shall replace any spare part that is missing and cannot be associated with a repair by specific unit number repaired.

Unless instructed otherwise by charterers, the Container Operator has to receive the Spare Parts Replacement Order no less than five working days before arrival. If less, the Container Operator can decide if the supply of any parts, along with the container, is possible. It is the Container Operator's responsibility to advise the vessel when replenishment of spare parts will take place and the date of delivery.