A pre-trip inspection is a structured check of a refrigerated trailer or container before any pallet goes on board. A driver or yard technician runs the reefer unit, checks the door seals, clears the drains and confirms the load space reaches its set point, all before a single case of product touches the floor. The check exists because a refrigerated vehicle looks the same whether the unit works or not. Only a box, run and inspected properly, proves it will hold temperature for the trip ahead.
The routine applies wherever a refrigeration unit hands off to a driver: a depot yard before a refrigerated road transport run, a container terminal before a reefer container moves inland, or a cross-dock between legs. Done properly it takes twenty to forty minutes, and it is the last point in the process where a fault costs nothing but time. Either a driver trained to run the checklist or a dedicated yard technician can carry it out, and larger fleets tend to push the job to a technician precisely so the driver is not the only person who ever laid eyes on the unit before departure.
The unit, set point and fuel
The technician starts the refrigeration unit and lets it run through a full cycle, watching the display for fault codes and confirming the compressor engages instead of just the fan. The set point gets checked against the load's actual requirement, not left on whatever the last shipment used: a unit still reading 2-8°C from a chilled run will not hold a frozen load at -20°C without a manual reset. Fuel level matters on diesel-powered units for any run over a few hours, since a unit that runs dry mid-transit stops cooling exactly like one that was never switched on. On electric standby units, the check shifts to battery charge and cable condition instead.
The unit also gets checked against the commodity, not just the number on the dial. A produce load tolerant of a wider band and a biologic shipment with a narrow one both show the same set point on the display if the driver types the wrong figure in, so the technician confirms the reading against the paperwork for that specific load before signing off, not against habit from the last trailer through the bay.
Door seals and drains
Rubber door gaskets harden and crack with age, and a gap the width of a pencil lets warm, humid air leak in every time the unit cycles. The technician runs a hand along the full perimeter of both doors, checking for tears, flat spots and a seal that actually compresses when the door latches. Drain plugs get checked too: a blocked drain lets condensation pool on the floor, refreeze around the load and soak pallets from below, none of which shows up until the doors open at the far end.
Airflow through the load space
An evaporator needs clear space to push air, and a clogged or iced coil cannot cool a trailer no matter how well everything else checks out. The inspection confirms the coil is free of frost buildup and debris, the floor channels or T-bar tracks are clear, and nothing is stacked against the bulkhead where the return air draws in. None of this guarantees a good load pattern once cargo goes on, but it rules out the unit itself as the point of failure before that cargo arrives.
The paper trail
Every check gets logged: unit run time, set point, fuel or battery level, seal and drain condition, and any fault code cleared or left open, with a name and a timestamp attached. That record travels with the shipment and backs up the temperature data logger readings taken in transit. If a claim comes in on a shipment that arrived warm, the pre-trip log is the first thing a shipper or insurer asks for, and a carrier with no record has no defence, whatever the unit actually did.
Some fleets shorten the check on a short shuttle run or a repeat backhaul, on the reasoning that a unit checked that morning does not need the full routine again a few hours later. That shortcut works right up until the one unit that develops a fault mid-shift, and a shortened check leaves no record proving the unit was sound at the point it left the yard the second time. A full check every time it changes hands costs a few minutes; a gap in the record costs the argument later.
A failed PTI beats a failed load
A unit that fails its pre-trip check in the yard is an inconvenience: a swap to another trailer, a delayed departure, a call to maintenance. The same unit failing three hours into a run is a lost load, a product write-off and a claim against the carrier. The inspection exists to move that failure to the cheapest possible point, before product is on board and before the clock on shelf life or contract delivery starts running. Skipping it to save time trades a small, certain cost for a much larger, uncertain one, which is why shippers moving anything perishable increasingly require a signed PTI record before they release a load to a carrier at all.