A Diesel Refrigerator
on a 53-Foot Frame.

Reefer is industry slang for a refrigerated trailer. It is a 53-foot insulated box with a diesel-powered refrigeration unit mounted on the nose. The unit does not blow cold into the trailer, it removes heat from the cargo space and vents it outside, holding any setpoint from deep frozen up to climate-protect warm. When a shipper says reefer freight or reefer trucking, they mean refrigerated transport.

A dry van is a bare, unconditioned box, so freight rides at whatever temperature the road serves up. A reefer adds about two to three inches of foam insulation, a ceiling air chute, and a diesel refrigeration unit that holds an exact setpoint in any weather. The reefer trailer costs roughly double, burns its own fuel, and carries slightly less payload, which is why reefer lanes price about 10 to 25 percent over a comparable dry van.

It is a closed refrigeration loop, not an air conditioner. A small diesel engine drives a compressor that pressurizes refrigerant. The gas dumps its heat through a condenser, turns liquid, passes an expansion valve, and boils in the evaporator coil inside the trailer, pulling heat out of the cargo space. Cold air is delivered from the top front, pushed down a ceiling chute, and returned along the floor, so the air does the cooling and the load has to be stacked to let it move.

It depends entirely on the load and the weather. A packed frozen load can coast many hours, even most of a day in cool weather, because of its huge cold mass. A light, respiring produce load can drift out of spec in under half an hour on a hot dock. Our Cold Chain Reaction-Window Simulator on this page models it: pick the commodity, the ambient, and the fill, and it estimates the window before product crosses its breach temperature. It is a planning estimate, not a guarantee, which is exactly why we monitor live.

From roughly April through July, fruit and vegetable harvests pull reefers toward produce origins like Salinas, McAllen, Nogales, and Yakima. Rejection rates climb, freight spills from contract into the spot market, and rates rise nationwide because the trucks leave everywhere else. The fix is booking ahead of the season instead of into it, which we plan for on recurring lanes.

Standard motor truck cargo insurance does not cover spoilage by default. Reefer breakdown is a separate endorsement that pays for temperature loss caused by mechanical or electrical failure of the unit. It explicitly excludes improper setpoint, driver negligence, bad or missing seals, and delay. We verify the endorsement is current before we tender, then manage the run so those excluded failure modes never get tested.

The unit displays return air, the air coming back along the floor to the unit, not the temperature of your product and not the cold air being discharged. During startup or under heavy summer load, return air can lag the setpoint. The number that actually matters is pulp temperature, what a probe reads inside the product, which is what the receiver checks at the dock. Knowing the difference between setpoint, return air, and pulp temperature is most of the job.

It can, but it should not for long. Every minute the doors are open without an air curtain floods the box with ambient heat and forces extra defrost cycles, and a long door-open dwell can break the cold chain before the truck even leaves. It is also why detention is expensive on reefer: the unit burns diesel the whole time it sits, on its own tank, so a slow dock costs fuel and risks the load at once.

In continuous mode the engine never stops and air never stops moving, which produce, fresh protein, dairy, floral, and pharma all require to carry off field heat and respiration heat. In Cycle-Sentry, the start-stop mode, the unit cools to setpoint, shuts off, and restarts when temperature drifts, which saves fuel and suits frozen and hardy freight. The run mode is an airflow decision, not just a fuel one, so we set it by commodity and write it on the tender rather than leaving it to the driver.