Refrigerated Freight in Winter: A Cold Chain Playbook for Shippers
Indeed, most cold chain failures are not equipment failures. They are loading-dock decisions made 15 minutes before the doors close. Here is what the FSMA Sanitary Transportation rule requires, what the refrigeration unit can and cannot do, and what changes when the temperature outside drops below freezing.
Key takeaways
- A refrigeration unit maintains product temperature — it does not change it. Freight loaded warm stays warm. Pulp temperature at the dock is the single highest-leverage control point in the entire chain.
- Pre-cool with the doors closed, then shut the unit off before opening them. Moreover, opening a pre-cooled trailer to humid ambient air causes ceiling condensation and cargo sweat.
- FSMA makes this a shared legal duty. The Sanitary Transportation rule covers shippers, loaders, carriers and receivers, and requires written procedures, agreements and training records — retained for periods not exceeding 12 months.
- Cycle-Sentry is not for tight-tolerance freight. Start-stop operation on temperature-critical cargo can cause hot spots and top freezing.
- Winter adds freeze protection, fuel gelling and chain laws. Colorado’s commercial chain law runs September 1 to May 31, with fines up to $500 plus a $79 surcharge — or $1,000 plus $157 if you block the road.
Why winter is the harder season
Shippers tend to worry about refrigerated freight in July. In practice, winter produces more claims, and for a less obvious reason: in winter the reefer unit frequently has to heat rather than cool.
For example, a trailer of bottled beverages crossing Wyoming in January needs to stay above 32°F, not below 40°F. Likewise, a load of fresh produce moving through a -10°F night risks freeze damage, not spoilage. The equipment handles both, but only if you choose the set point, the mode and the load plan with the right direction of heat transfer in mind — and only if the driver knows which risk they are managing.
Winter also compounds every other problem. Doors stay open longer because dock workers move more slowly. Diesel gels. Road closures turn a 10-hour run into a 30-hour one. Moreover, the products that move most often in winter — beverages, canned goods, liquids, paints, pharmaceuticals — are often freezables, where a single overnight dip below 32°F destroys the entire load.
What FSMA actually requires
The FDA’s Sanitary Transportation of Human and Animal Food rule, issued under the Food Safety Modernization Act, applies to shippers, receivers, loaders and carriers who transport food in the United States by motor or rail vehicle — including parties shipping directly into the U.S. from Canada or Mexico. Ship and air transport are not covered.
It sets out four areas of requirement:
- Vehicles and transportation equipment. Must be suitable and adequately cleanable for their intended use, and capable of maintaining the temperatures needed for safe food transport.
- Transportation operations. Measures to ensure food safety in transit — temperature control, prevention of cross-contamination between raw and ready-to-eat foods, and protection against allergen cross-contact.
- Training. When the carrier is responsible for sanitary conditions, it must provide food safety training to personnel and document that training.
- Records. You must also keep written procedures, agreements and training documentation, with retention periods not exceeding 12 months.
However, exemptions include operations with less than $500,000 in average annual revenue, farm transportation activities, food in completely enclosed containers (except where temperature control is required for safety), live animals, and food transshipped through the U.S. to another country.
Pre-cooling the trailer correctly
Pre-cooling removes residual heat from the trailer structure itself — walls, floor, ceiling, doors — so that heat is not transferred into the cargo after loading. Still, done properly it takes less than two hours.
The procedure that matters, and the one most often got wrong:
In short, the reason is physics, not procedure for its own sake. A pre-cooled trailer opened to warm, moist ambient air pulls that air in and condenses it on every cold interior surface. You get water on the ceiling, which drips onto the top layer of cartons, and cargo sweat on the cases themselves. In humid conditions this ruins corrugated packaging and creates exactly the food safety conditions the whole exercise was meant to prevent. Running the unit while the doors are open makes it worse, because the unit actively draws the humid air in.
Pre-trip discipline: before departure the unit should be run in high-speed cool for at least 20 minutes and pass an automatic pre-trip test, with the set point confirmed against the shipper’s written instruction and the operating mode double-checked. Documenting the time and date of that pre-trip is one of the most valuable pieces of paper you will have if a claim is ever filed.
Pulp temperature at the dock
This is the sentence to remember, and it is the one most commonly violated in practice:
Therefore, product should arrive at the loading dock already at its intended shipping temperature. A trailer reefer has nothing like the capacity of a blast chiller; asking it to pull 15 degrees out of a full load of palletized produce will take days it does not have, and will do so unevenly, freezing the pallets nearest the discharge air while the centre of the load stays warm.
So measure. Use a calibrated probe thermometer to take internal product readings before loading, and take them in more than one place — take readings from the nose, middle and tail sections as the load goes on. Record them. If pulp temperature is out of specification, that is a conversation to have on the dock, not a problem to hand to the driver.
Loading patterns and airflow
Above all, a reefer works by circulating air, not by chilling the surfaces it touches. If the air cannot move around the load, the load will not hold temperature no matter how good the unit is. Practical requirements:
- Minimum 3 inches of clearance between the load and the sidewalls.
- At least 9 inches between the top of the load and the ceiling, so discharge air can reach the tail of the trailer.
- Moreover, centerline loading works best, and airbags or foam blocks stop the load shifting into the walls.
- Four-way pallets with unrestricted openings, so air can move through the base of the load as well as around it.
- No plastic wrapping around respiring cargo. For instance, fruit and vegetables generate heat and need air exchange; shrink-wrapping them traps it.
- Use the air chute where fitted, and check it is not torn or collapsed — it is what carries discharge air to the back of the trailer.
Floor drains and T-flooring matter too. If the drains are blocked or the load sits flat on the floor rather than on the T-rails, return air cannot get back to the unit and the load effectively insulates itself.
Continuous vs. cycle operation
Modern reefer units can run continuously or in a start-stop mode (Thermo King markets this as CYCLE-SENTRY; Carrier as Start-Stop). Meanwhile, cycle operation saves fuel and reduces engine hours by shutting the unit down once it reaches set point and restarting when it drifts.
That is appropriate for frozen freight with thermal mass and wide tolerance. It is not appropriate for tight-tolerance cargo. The Global Cold Chain Alliance is direct about it: operating on CYCLE-SENTRY with cargo requiring tight temperature control is not recommended and can result in product hot spots and top freezing.
| Mode | Use for | Avoid for |
|---|---|---|
| Continuous run | Fresh produce, dairy, fresh meat, pharmaceuticals, anything with a narrow tolerance or a requirement for constant airflow | Nothing on safety grounds — only a fuel cost consideration |
| Cycle / start-stop | Deep frozen freight with wide tolerance and high thermal mass | Fresh produce, any load with a tolerance under roughly ±3°F, any respiring commodity |
Specify the mode on the rate confirmation. “Continuous run, set point 34°F” is an instruction. “Keep it cold” is not.
Typical set points by commodity
The table below reflects commonly used industry set points. It is a planning reference only — always defer to the shipper’s written specification, which governs.
| Commodity | Typical set point | Notes |
|---|---|---|
| Most fresh produce | 34–38°F | Continuous run; respiring, so no plastic wrap |
| Bananas and tropical fruit | 56–58°F | Chill injury below about 55°F |
| Potatoes and onions | 45–50°F | Freeze and sweeten at low temperatures |
| Dairy | 34–38°F | Continuous run |
| Fresh meat and poultry | 28–32°F | Narrow window; monitor closely |
| Frozen food | 0°F or below | Cycle operation usually acceptable |
| Ice cream and frozen desserts | -10 to -20°F | Continuous run; very intolerant of drift |
| Chocolate and confectionery | 55–65°F | Bloom risk from temperature swings |
| Cut flowers | 33–35°F | High airflow requirement |
| Freezables (beverages, canned goods, liquids) | Protect from freeze, above 32°F | Winter heat mode; the classic cold-weather claim |
Winter-specific operations
Freeze protection and heat mode
For freezables, the instruction is not a cooling set point at all — it is a floor. The unit runs in heat mode to hold the box above freezing. Confirm before dispatch that the unit’s heat function has been tested in the pre-trip, because a cooling-only failure stays invisible until the load is already north of the snow line.
Diesel gelling and fuel management
Number 2 diesel begins to cloud and gel as temperatures fall, and a reefer unit has its own fuel tank that is easy to overlook. Winter practice: run a winter blend or an anti-gel additive appropriate to the region, keep the reefer tank full to reduce condensation, and check fuel filters and any filter heater during pre-trip. A reefer that shuts down on a gelled filter at 3am is a total loss on a fresh load.
DEF in cold weather
Diesel exhaust fluid freezes at roughly 12°F. Still, this is expected and does not damage the fluid or the system — tractor DEF tanks and lines carry their own heaters and thaw during operation. What matters is not attempting to dilute DEF or use additives, which will trigger emissions faults.
Hours of service in adverse conditions
FMCSA rules allow a driver to extend both the 11-hour driving limit and the 14-hour window by up to 2 hours when adverse driving conditions arise. That is a genuine operational buffer for unexpected weather — but it is an exception for conditions nobody could have known at dispatch, not a planning tool. Building a schedule that only works when a driver uses that exception is how drivers end up out of hours in a snowstorm.
Chain laws
Western mountain states enforce chain requirements on commercial vehicles seasonally. Colorado is a useful benchmark: its commercial motor vehicle chain law applies to vehicles over 16,000 lbs GVWR/GCWR on specified routes from September 1 to May 31. Straight trucks, tandem combinations and auto transporters must carry four tire chains or approved alternate traction devices for the drive wheels. Violations carry fines of up to $500 plus a $79 surcharge, rising to $1,000 plus a $157 surcharge if the vehicle blocks the roadway.
Requirements vary by state and by route, so confirm the current rules for every lane you run in winter rather than assuming Colorado’s thresholds apply everywhere.
Monitoring and documentation
Real-time telematics should collect data every 5 to 15 minutes, capturing compartment air temperatures, GPS location, door status and fuel level. Temperature deviations should trigger event notifications so somebody can take corrective action while the load is still recoverable — a download you read after delivery only tells you how the claim happened.
Keep the following for every temperature-controlled load:
- Pre-trip record with date, time and result of the automatic pre-trip test
- Pre-cool start time and trailer temperature at the point of loading
- Pulp temperatures at nose, middle and tail, with the instrument used
- Set point and operating mode as instructed, in writing
- Continuous temperature log or telematics download for the full transit
- Door-open events and their duration
- Delivery receipt with product temperature at unload and any exceptions noted
Preventing and surviving claims
Moreover, whichever party holds the better documentation usually wins a temperature claim, whatever actually happened. The practical defence is the same set of records listed above, captured routinely rather than assembled after the fact.
Three habits prevent most disputes outright: measure and record pulp temperature at loading so the dock establishes responsibility for warm product; put the set point and operating mode in writing on the rate confirmation so there is no ambiguity about the instruction; and note exceptions on the delivery receipt at the time of unload, because a clean signed receipt is very hard to challenge a week later.
If you are still deciding how to move the freight, our FTL vs. LTL guide covers mode selection, and our carrier vetting checklist covers what to verify before you tender a temperature-controlled load to anyone.
Frequently asked questions
Whose responsibility is pre-cooling, the shipper’s or the carrier’s?
Whoever the written agreement says. FSMA expects the parties to assign responsibility explicitly, and leaving it unstated is precisely the gap that produces disputes. In common practice the carrier pre-cools the trailer and the shipper is responsible for delivering product at the correct pulp temperature — but write it down.
Does my small operation fall under the FSMA transportation rule?
Operations with less than $500,000 in average annual revenue are exempt, as are farm transportation activities, live animals, food in completely enclosed containers where temperature control is not required for safety, and food transshipped through the U.S. to another country. Exempt from the rule is not the same as exempt from liability under your contract, however.
How long do I need to keep the records?
In addition, FSMA requires you to keep written procedures, agreements and training documentation, with retention periods not exceeding 12 months. Many shippers keep temperature logs longer than that to match their own claim windows and customer requirements.
Can a reefer bring warm product down to temperature in transit?
Not reliably, and you should not plan for it. In short, the unit maintains temperature; it does not remove field heat. Attempting it produces uneven results — freezing at the discharge end while the centre of the load stays warm — and in most contracts it shifts liability to whoever loaded the product warm.
What is top freezing and how do I avoid it?
Top freezing is damage to the upper layer of a load caused by cold discharge air hitting product directly, often when a unit cycles hard to recover set point. Therefore, you avoid it by keeping at least 9 inches of ceiling clearance, using an intact air chute, and running continuous rather than cycle mode on tight-tolerance freight.
What should a shipper put on the rate confirmation for a reefer load?
So at minimum, specify the set point in degrees Fahrenheit, operating mode (continuous or cycle), whether the load needs pre-cooling and to what temperature, pulp temperature tolerance at loading, whether the load is a freezable requiring heat protection, and the temperature logging or download required at delivery.
Sources
- U.S. Food and Drug Administration, FSMA Final Rule on Sanitary Transportation of Human and Animal Food.
- Global Cold Chain Alliance, Refrigerated Transportation Best Practices Guide (PDF) — pre-cooling, pulp temperature, airflow clearances and operating mode.
- Federal Motor Carrier Safety Administration, Summary of Hours of Service Regulations — adverse driving conditions exception.
- Colorado State Patrol, Chain Law Information — commercial vehicle requirements, seasonal dates and penalties.
Related reading
Moving temperature-sensitive freight this winter?
Our refrigerated fleet runs documented pre-trips, continuous-mode dispatch on tight-tolerance loads and full temperature logging on every shipment.