Trailer Refrigeration Units

Proper TRU maintenance

Keeping transport refrigeration units (TRUs) well maintained and performing at peak operating condition is an important aspect of a reliable cold chain that safely delivers produce, meat, seafood, frozen foods, pharmaceuticals and many other products. A solid maintenance program not only helps protect refrigerated cargo, it also alleviates many unanticipated equipment failures that can lead to the expensive consequences of load losses.

Engineering and design improvements have made today’s TRUs - commonly referred to as reefers - more operationally sophisticated, fuel efficient, environmentally sound, and, from a service perspective, more durable and reliable. But these improvements, while beneficial to the overall goal of delivering refrigerated cargo safely and on time, should never take the place of a disciplined maintenance strategy.

While this maintenance overview is based on current Carrier Transicold trailer refrigeration equipment, procedures can vary among different generations of equipment and different manufacturers. As with any piece of mechanical equipment, manufacturers’ guidelines for the specific equipment should always be followed.


The Carrier Transicold TRU family includes both conventional mechanical refrigeration units, as found in the X2 series, and hybrid diesel-electric units, known as the Vector family.

Hybrid units have a streamlined, all-electric refrigeration architecture that eliminates many of the routine maintenance components found in conventional belt-driven refrigeration systems. By eliminating such components, Carrier specifically designed the units for lower lifecycle costs.

Based on service history, the average amount of time required to service a hybrid unit is at least 25 percent less than a conventional belt-driven unit. Over the life of the unit, the hybrid TRU can result in a reduction of up to 30 percent in total maintenance costs, as tracked by Carrier Transicold’s Aftermarket Solutions group.

For example, the hybrid unit’s electric refrigeration system does away with all but one of the many belts and pulleys that drive a conventional system. In place of this mechanical assembly is a high-performance generator powered by the unit’s diesel engine.

Evaporator and condenser fans are driven by maintenance-free electric motors, rather than belts. Also, the electrically driven semi-hermetic compressor eliminates the compressor driveshaft and associated wear and leak concerns of a shaft seal.

The all-electric architecture of the hybrid Vector unit also eliminates maintenance items, such as the suction and discharge vibrasorbers, alternator, mechanical clutch, gearbox, mechanical fan shaft and some of the refrigeration valves.

For heating, Vector systems depart from conventional hot gas and instead use electric-resistance strips, resulting in a streamlined refrigeration circuit that uses less refrigerant.

A hybrid unit’s diesel engine still requires periodic inspections and benefits from preventive maintenance, much the same as conventional units. But over the life of the unit, there are fewer parts to deal with and reduced concerns about such issues as a mechanical failure due to something as simple as a broken or thrown belt.


For both conventional and hybrid TRUs, recommended daily checks include oil and coolant levels, a visual check for leaks of any kind, inspection to ensure that the belts are tight, and listening for unusual noises when the unit is running.

On start-up, the microprocessor will run a self-test of the system electronics and its display will show whether any alarm conditions are detected or whether any conditions had previously been detected that require checking at the next service interval.

Before hitting the road, the unit microprocessor is also capable of running a pre-trip routine that analyzes full unit operation and tests over 15 critical functions in about eight minutes.

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