What temperature should a reefer trailer run at for different cargo types?

Temperature setpoints vary by cargo type. Deep frozen goods (ice cream, fish, meat): −18°C to −20°C minimum — the ATP Class C definition. Chilled meat and dairy: 0°C to +4°C. Fresh produce (fruits, vegetables): +4°C to +8°C depending on the specific commodity — bananas require +12°C to +14°C, for example, while strawberries need +1°C to +2°C. Pharmaceutical products: typically +2°C to +8°C (CRT — controlled room temperature) or +15°C to +25°C depending on the drug. Always follow the shipper's or manufacturer's specified temperature range — the reefer setpoint is a contractual requirement, not a guideline.

What is an ATP certificate and when is it required?

The ATP certificate (Agreement on the International Carriage of Perishable Foodstuffs) is a document confirming that a reefer trailer meets the thermal performance standard required for carrying perishable goods internationally. It is required for all international road transport of perishable foodstuffs between the 50+ countries that have ratified the ATP agreement, which includes all EU member states. The certificate specifies the ATP class (A for chilled, C for deep frozen), the K-coefficient (insulation efficiency), and the expiry date. Certificates are valid for 6 years from first issue and must be renewed after a physical test of the trailer's thermal performance. For domestic transport, national rules vary — some countries require ATP for domestic movements of frozen goods.

How long does it take to pre-cool a reefer trailer?

Pre-cooling time depends on the ambient temperature, the target setpoint, and the starting temperature of the trailer interior. As a practical guide: for a +4°C setpoint starting from +20°C ambient, allow 2–3 hours. For a −18°C setpoint starting from +20°C ambient, allow 4–6 hours. These times assume the reefer unit is functioning correctly and the trailer has reasonable insulation. In summer (ambient above +30°C), add 30–60 minutes. Pre-cooling should start with the doors closed — opening the doors to speed cooling is counterproductive and wastes energy. The correct check: verify the return air sensor (not the discharge sensor) reads within 1–2°C of setpoint before accepting cargo.

Can I mix fresh and frozen cargo in the same reefer trailer?

In a standard single-temperature reefer trailer, you cannot safely mix fresh produce (typically +4°C to +8°C) and deep frozen goods (−18°C). Running at the frozen setpoint would freeze the fresh produce; running at the chilled setpoint would thaw the frozen goods. Multi-temperature reefer trailers with a physical bulkhead dividing the trailer into two separately controlled zones can carry both simultaneously, with the frozen zone at the front (closest to the evaporator) and the chilled zone at the rear. Without a multi-temp bulkhead, mixing temperatures is not possible. For single-temperature trailers, the load must be entirely within one temperature band.

What causes temperature excursions in reefer transport and how do I prevent them?

The most common causes of temperature excursions in reefer transport are: loading warm cargo that the reefer cannot cool (the reefer maintains temperature, it does not create it); blocked return air ducts preventing circulation; excessive door-open time at loading or delivery stops; reefer unit breakdown or fuel run-out; and damaged insulation (cracks in walls or floor). Prevention: always verify cargo pulp temperature before loading; never block the floor T-bar or return air duct; minimise door-open time and use strip curtains; check reefer fuel level and unit service history before departure; inspect trailer seals and insulation condition at pre-trip. Temperature data loggers that send real-time alerts allow you to intervene during transit — without a logger, a temperature excursion may only be discovered at delivery.

Cold Chain Guide

Reefer Trailer Loading Guide

A reefer trailer is not just a refrigerator on wheels — it maintains temperature by circulating air, not by cooling the cargo directly. Load it wrong and no amount of refrigeration will save the shipment.

Deep frozen setpoint

−18°C to −20°C

Chilled setpoint

+2°C to +6°C

ATP certificate

Mandatory EU

Trailer length

13,600 mm

Temperature Mode Selector

Select a cargo type to see setpoint, pre-cool time, and loading rules

CAB

UNIT

air

🚪

−25°C

+25°C

Setpoint

+4°C to +8°C

Pre-cool time

2–4 hours

Humidity control

85–95% RH

Max door-open time

≤ 30 min

Continuous circulation — never block floor T-bar ducts

Cold Chain Guide

How to load a reefer trailer for cold chain transport

Every step in this sequence matters. A single thermal bridge, blocked duct, or warm cargo pallet can compromise the entire load — even if the reefer unit runs perfectly throughout.

Step 1

Pre-cool the trailer — minimum 2 hours before loading

A reefer unit cannot cool warm cargo — it can only maintain a pre-established temperature. The trailer interior walls, floor, and ceiling must be pre-cooled to the target setpoint before any cargo enters. For fresh produce at +4°C, allow at least 2–3 hours. For deep frozen at −18°C, allow 4–6 hours. Check the setpoint temperature at the return air sensor — not the discharge air. If the trailer has been standing in direct sun, add 30–60 minutes to these times. Never accept a trailer that has not been pre-cooled to within 1–2°C of setpoint.

Step 2

Verify cargo temperature before loading

Only pre-cooled cargo may enter a pre-cooled trailer. Loading warm or partially thawed cargo — even a single pallet — will raise the trailer temperature and force the reefer unit to work against an internal heat source it cannot overcome. Check pulp temperatures with a calibrated probe: for fresh produce, pulp temp must match or be within 1–2°C of setpoint. For frozen goods, every pallet must be at −18°C or below — if any pallet is partially thawed, reject it and document. Warm cargo entering a cold trailer is the single most common cause of cold chain failure.

Step 3

Load to maintain airflow — never block the T-bar floor or return air duct

Reefer trailers maintain temperature through forced air circulation: cold air is delivered from the front (evaporator unit) along the ceiling, flows down the sides and rear, circulates along the floor T-bar channels, and returns to the evaporator via the return air duct at the front floor. This path must remain unobstructed. Load on pallets — never directly on the floor — so air can flow under and around cargo. Never stack cargo against the front bulkhead or over the return air duct. Never load cargo that reaches the ceiling: leave at least 100–200 mm of headspace for air circulation. A blocked return air duct causes a warm spot at the return that will trigger false alarms and thermal runaway in the rear of the trailer.

Step 4

Set continuous airflow mode — not start/stop

Most reefer units have two airflow modes: continuous (fan runs permanently) and start/stop (fan cycles with the compressor). For temperature-sensitive cargo — pharmaceutical, fresh produce, any load with tight tolerances — always use continuous mode. Start/stop mode reduces fuel consumption but allows micro temperature fluctuations as the fan idles between compressor cycles. For frozen bulk cargo with wide tolerance (±3°C acceptable), start/stop is acceptable. For fresh produce or pharma, the ATP agreement or customer specification typically mandates continuous mode. Check the mode setting before closing the doors.

Step 5

Minimise door-open time — use curtain strips if available

Every time the rear doors are opened, warm ambient air floods the trailer. In summer, a 25°C ambient against a −18°C trailer interior creates an immediate condensation and temperature rise that takes 10–20 minutes of compressor run time to recover. Pre-plan every door-open event: have all cargo for that unloading ready before opening doors. Use plastic strip curtains on the door opening if the facility does not have a dock seal. Brief the forklift operator — they must work at pace. For pharmaceutical loads, door open times must be logged and submitted with the GDP documentation. Maximim door open time at each stop: fresh produce ≤ 30 min, frozen ≤ 20 min, pharma ≤ 15 min.

Step 6

Set up temperature data logger and complete ATP documentation

A calibrated temperature data logger (or the built-in reefer telematics) must record the setpoint, actual temperature, and any alarms throughout the journey. For pharmaceutical transport under GDP guidelines, the logger is mandatory and the data must be reviewed before release of the goods. For ATP-regulated transport in Europe, the reefer unit must hold a valid ATP certificate confirming its thermal performance. Check the ATP plate on the trailer — expired ATP means the trailer cannot legally carry perishable goods across EU borders. At delivery, download the temperature record and provide it to the consignee as proof of cold chain integrity.

Cold Chain Regulations

Reefer transport rules at a glance

Based on ATP Agreement (perishable goods), EU Regulation 37/2005 (temperature monitoring), GDP guidelines (pharmaceutical), and EC Directive 96/53 (vehicle dimensions).

Deep frozen setpoint

−18°C

Minimum, ATP Class C

Chilled setpoint

+2°C to +6°C

Fresh produce / dairy

ATP certificate

Required EU

Renewed every 6 years

Max GVW

40,000 kg

Standard EU 5-axle

ATP certificate requirement

Mandatory for perishable goods

The ATP Agreement (Agreement on the International Carriage of Perishable Foodstuffs) requires that reefer vehicles used for international transport of perishable foodstuffs carry a valid ATP certificate. The certificate confirms the trailer's insulation efficiency (K-coefficient) and refrigeration capacity. ATP class definitions: Class A — mechanically refrigerated, Class C — deep frozen (−20°C). ATP certificates are valid for 6 years from first issue, then must be renewed after testing. An expired ATP certificate prohibits international carriage of perishable goods — verify the ATP plate date before every international trip.

Return air duct clearance

Never block

The return air duct at the front floor of the trailer is the intake for the refrigeration circuit. If blocked — by cargo, a fallen pallet, or directly-stacked boxes — the evaporator draws warm air from around the blockage instead of from the rear of the trailer. The result: the front of the trailer over-cools (ice build-up on evaporator coils) while the rear warms up. This is the most common technical cause of cold chain failure that is not a reefer unit malfunction. Always load on pallets, never floor-stack, and always leave the front 600 mm of floor clear of cargo.

GDP pharmaceutical transport

Validated cold chain required

Pharmaceutical products subject to GDP (Good Distribution Practice) guidelines require a validated cold chain with documented evidence. This means: a calibrated temperature data logger with a certificate of calibration, a temperature mapping study for the specific trailer and route profile, a qualification protocol for the reefer unit, and deviation reporting for any temperature excursion. GDP also requires driver training on cold chain procedures and a written agreement (Technical Quality Agreement) between the pharma manufacturer and the logistics provider. Standard reefer documentation is not sufficient for GDP-regulated products.

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