Container Reefer Unit

What a container reefer unit is, on board a ship

A reefer container carries its own complete refrigeration plant built into one end of the box - compressor, condenser, evaporator and controller - rather than relying on the ship's own cooling system. The ship's role is limited to supplying three-phase electrical power to each container's socket and, on a purpose-built container or reefer vessel, forced air circulation through the hold for the units' condenser cooling; the ship does not refrigerate the cargo itself. This is what separates a reefer container from the fixed provisions cold rooms elsewhere on the same ship, which share one central plant.

Main components

Integral machinery package

Compressor, condenser and evaporator fan section built into the container's front wall, drawing power through a standard reefer plug at the container base or top depending on design.

Microprocessor controller

Holds setpoint, records temperature history for the voyage, and on modern units reports remotely to shore or ship monitoring systems - this logged data is what a shipper relies on to prove the cargo was kept in range.

T-bar floor and air delivery

A ridged floor under the cargo creates an air channel so cooled air is forced up through the load rather than just around it, essential for perishables packed to the door.

Controlled/modified atmosphere option

Some units add CO2 and O2 control for produce that needs a modified atmosphere in transit, on top of straight temperature control.

Selection and sizing

Selection is less about physical sizing, since reefer containers come in standard TEU/FEU dimensions, and more about matching refrigerant type, controller generation and monitoring compatibility to the operator's fleet and the ship's power and monitoring infrastructure. Vessels with a dedicated reefer monitoring system need units whose controllers speak the same protocol, or a conversion plug, to get remote alarm and temperature data rather than relying on deck rounds alone.

Regulations and class

Refrigerant selection is under increasing pressure from the Montreal Protocol and IMO GHG-related instruments driving fleets away from high-GWP refrigerants toward lower-impact alternatives. Power supply and socket arrangements on the ship side fall under the vessel's electrical classification, and reefer plug circuits typically carry their own overload and ground fault protection separate from the main ship's power distribution.

Typical faults

• Loss of ship power to the socket - a tripped breaker or damaged plug/socket connection stops the unit cold regardless of the container's own condition, and is the single most common cause of a reefer excursion at sea.
• Condenser airflow restriction - stacking or lashing gear blocking the condenser grille raises head pressure and can trip the unit on high pressure protection.
• Controller sensor drift - a return-air or supply-air sensor reading incorrectly can hold the unit on setpoint by its own display while the actual cargo temperature drifts.
• Door seal or drain blockage - lets in humid air or traps meltwater, both of which damage delicate produce even with the refrigeration plant working correctly.

What to look for in a supplier

• Controller and monitoring protocol compatible with the operator's existing reefer monitoring system.
• Refrigerant type aligned with current and near-term environmental regulation, not a soon-to-be-restricted charge.
• Service network and spare parts availability across the actual ports the containers move through, not just the country of manufacture.

Before opening up a faulty reefer container, check the socket and breaker on the ship side first - a large share of reported unit failures turn out to be a power supply problem at the plug.