Equipment / Trailers
Reefer in trucking
Plain-English explanation
A reefer is a refrigerated trailer equipped with a diesel-powered refrigeration unit that can heat or cool the trailer interior to maintain a specified temperature range. Reefer trailers carry freight that cannot travel at ambient temperature: fresh and frozen produce, meat and poultry, dairy products, pharmaceuticals, flowers, certain chemicals, and any other commodity where temperature deviation causes product loss or rejection. The refrigeration unit on a reefer trailer operates independently of the truck engine and runs on its own diesel tank. Drivers must monitor the reefer fuel level the same way they monitor the truck fuel level — running out of reefer fuel during transit can result in a full load rejection if the product temperature climbs above the specified range. Reefer fuel stops are a regular part of trip planning on long runs. Refer freight moves under specific temperature instructions that appear on the rate confirmation and the BOL. The two primary operating modes are: **Continuous** — the reefer runs constantly to maintain a set temperature. Common for produce, fresh meat, and other perishables where any temperature deviation is a problem. **Cycle/Sentry** — the reefer cycles on and off to maintain a temperature range rather than holding a constant set point. Common for frozen freight and commodities where the target is a stable range rather than a precise degree. Before pickup, the driver or dispatch needs to confirm the set point temperature, whether the trailer needs to be pre-cooled before loading, and whether the load requires continuous or cycle mode. Some shippers will refuse to load a trailer that has not reached the target temperature, and the driver may have to run the reefer for an hour or more before the shipper will open the doors. After pickup, the driver records the temperature setting, the departure temperature, and the reefer fuel level on the trip paperwork. Many reefer loads require a temperature download — a printout from the reefer unit showing the temperature log throughout transit. This download is what the consignee uses to verify that the freight was maintained within the specified range from pickup through delivery.
For reefer freight, the definition is only half the work. The driver and office also need the set point, run mode, fuel level, pre-cool status, and temperature documentation.
Why it matters in trucking
Reefer loads have more ways to go wrong than dry van loads, and the consequences of a problem are usually a rejected or damaged load worth multiples of the freight revenue. A rejected pharmaceutical load or a rejected produce load can result in a cargo claim that far exceeds what the carrier earned for hauling it. Pre-trip confirmation of set point, pre-cool status, reefer fuel, and unit alarm status is not optional — it is the difference between a completed load and a liability.
Temperature-controlled freight leaves less room for vague notes. A missing set point or unclear reefer instruction can become a claim problem later.
Example in real use
A carrier hauls a load of fresh strawberries from California to a distribution center in Atlanta. The rate confirmation requires the trailer to be pre-cooled to 34°F before loading, the reefer to run continuous, and a temperature download to be provided at delivery. The driver confirms the trailer is at 34°F before backing into the shipper's door, verifies reefer fuel before departure, monitors temperature on the unit display during transit, and prints the temperature log at the consignee before unloading. The download shows the load held 34–36°F throughout transit; the consignee accepts the freight.
How to keep temperature freight out of trouble
A reefer load should be checked before the truck reaches the shipper. The driver needs the set point, pre-cool instruction, run mode, fuel plan, and what to do if the unit alarms. Dispatch should not assume the shipper will load a trailer that is close enough.
Temperature claims often start with small gaps in the record. Save temperature instructions, reefer fuel receipts when useful, seal notes, pulp-temp instructions, and any receiver exception. If the unit alarms, report it quickly and keep the timeline.
Reefer checks
- Set point, acceptable range, and continuous or start-stop mode.
- Pre-cool status before arriving at pickup.
- Reefer fuel, unit alarms, door seals, and trailer condition.
- Temperature notes on BOL, app, or receiver paperwork.
Where it shows up
Reefer details show up before pickup, during transit, and at delivery. Temperature instructions should be treated as load requirements, not background notes.
What to check first
- Set point, acceptable temperature range, and continuous or start-stop mode.
- Pre-cool requirement and whether the trailer must be at temp before arrival.
- Reefer fuel level, unit alarms, and door-seal condition.
- Temperature records, pulp-temp notes, and receiver exceptions.
Common mistakes or confusion
- Not pre-cooling the trailer before arriving at the shipper — shippers who load into a warm trailer may reject the driver and reschedule the pickup, creating appointment and detention complications.
- Missing the temperature instructions on the rate confirmation — continuous versus cycle mode, set point, pulp temperature requirement, and pre-cool are all specified on the paperwork and should be read before dispatch.
- Not monitoring reefer fuel during long runs or not knowing where reefer fuel stops are available — a reefer that runs out of fuel during transit can allow temperature deviation that results in load rejection at delivery.
Related terms
Commonly confused with
Related guides
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Sources and last updated
Last updated: 2026-05-10