How complicated can it be? Isn’t it just a trailer that runs like a refrigerator?

Image: Utility 3000R with Thermo King S-600 Reefer Unit

True, to a certain degree. There are a lot of variables when it comes to a refrigerator that moves through different weather, varying temperatures from day and night, and how well the product holds the temperature.

Image: Thermo King Precedent S-600 by Thermo King

Types of refrigerated Temperature settings: Continuous & Cycle Sentry


Although this is energy intensive, it provides the most protection of your product while in transit. The produce industry requires that the continuous setting must be used when transporting fruits and vegetables. Produce needs continuous air flow to handle the product respiration and to keep consistent temperature throughout the trip. The reefer unit would have a “Set Point” that is manually set by the driver, and have it run at the specified temperature as instructed on the Bill of Lading (BOL) to prevent product damage.

The continuous setting will have a defrost cycle to remove ice or frost buildup from the coil. These units typically have an automatic defrost based on the temperature difference it detects, but otherwise would run a cycle every 6 hours by default. This should not affect the product being transported since the ambient temperature will change faster than the temperature of the product, and the cycle would shut off before it becomes a problem.

Cycle-Sentry Mode

Commonly used to transport chilled and frozen products, this setting saves fuel and reefer hours. Carriers prefer this setting since it extends the life of the reefer unit, which is fairly expensive to maintain, repair and eventually replace. The driver would set a temperature, and the reefer unit would turn on and shut off as it automatically manages the ambient temperature of the trailer.

Running the reefer on cycle-sentry has risks associated with it, since the temperature would have minor fluctuations as the air isn’t continuously flowing. To mitigate some of the risks of running cycles, one method would be to have the reefer unit run every “x” minutes for “y” minutes regardless of the current temperature. This would in turn, still save significant fuel and reefer hours, while keeping the product being transported at temperature.

Tips Moving Temperature Controlled Freight

  • Frozen products generally stay cold longer than chilled product without the refrigeration unit running, which in turn leads to less fuel usage and fewer reefer hours being used.
  • Transporting product that is refrigerated, but not frozen, through areas with freezing temperatures, the trailer is actually heating up the trailer to keep the product from freezing.
  • The frequency of opening the trailer doors will affect the temperature, and may cause fluctuations on the temperature recorder. This will happen when there are multiple stops.
  • To move refrigerated freight in California, the reefer unit must be CARB compliant. Most approved units have 7 years of compliance before it needs to be replaced, and some units are approved for its lifetime because the emissions meet the special requirements of the regulations.

How Often Should I Check the Reefer Temperature?

Older reefers need routine servicing usually every 1,000 hours, while newer ones need to be serviced at least every 1,000 hours. The reefer temperature should be checked regularly, to make sure the correct temperature is maintained.

Need Refrigerated Trucking Services?

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“We are the protectors of clients’ dreams by getting their creations to market at the right time for maximum effect.”

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