TRU (Transport Refrigeration Unit)
A transport refrigeration unit (TRU) is a diesel or electric refrigeration system mounted on a truck, trailer, or intermodal container that maintains cargo temperature during transit.
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Compare Telematics software →What a TRU Is and How It Fits Into Fleet Operations
A transport refrigeration unit (TRU) is the self-contained cooling or heating system that maintains temperature control inside a refrigerated truck, trailer, or container. Unlike a building HVAC system that draws from a power grid, a TRU carries its own diesel engine or connects to the vehicle's electrical system to generate the refrigeration it needs while moving. TRUs are a distinct maintenance responsibility from the tractor or truck — they have their own engine hours, fluid schedules, and failure modes — and are a critical component of any cold chain fleet operation.
Most TRUs are trailer-mounted and run on an independent diesel engine that operates regardless of whether the tractor engine is on or off. This is intentional — the TRU must maintain temperature at loading docks, during driver breaks, and when the trailer is dropped. A key distinction for fleet monitoring: TRU engine hours and tractor engine hours accumulate independently, which is why TRU maintenance schedules are tracked separately in fleet maintenance software. A trailer with 15,000 tractor miles may have 8,000 TRU engine hours — the TRU is the higher-wear component.
TRU monitoring in modern fleet telematics platforms goes beyond temperature logging. Advanced TRU monitoring includes: set-point vs. return-air vs. cargo probe temperature (three distinct readings that together indicate cooling performance); door sensor events (when the cargo door opens, temperature risk starts); defrost cycle tracking; fuel consumption of the TRU engine separately from the tractor; and fault codes from the TRU controller. Carriers operating in California must also comply with CARB's TRU regulations, which set emissions standards for TRU engines based on model year and require annual inspection certifications.
The move toward electric TRUs is accelerating in urban delivery fleets. Battery-electric TRUs eliminate direct TRU emissions (important for zero-emission zones and CARB compliance), reduce noise during night deliveries, and lower fuel costs. However, battery-electric TRUs add charging infrastructure requirements — either shore power at the depot or on-board solar — and have limited range for long overnight transit. Most long-haul refrigerated carriers still use diesel TRUs for their range and reliability. Fleet management platforms increasingly offer TRU integration alongside GPS tracking and driver ELD compliance in a single dashboard.
- Track TRU engine hours separately from tractor miles — TRU PM schedules are based on hours, not mileage
- Set pre-trip temperature verification requirements — confirm TRU reached set-point before cargo is loaded
- Monitor set-point, return-air, and cargo probe temperatures in real time during transit
- Log all door open events during transit and correlate with temperature trend data
- Maintain CARB TRU compliance documentation for California operations (annual inspection, emissions tier records)
- Evaluate electric or hybrid TRU options for urban routes and overnight dock operations to reduce CARB exposure