Most of us are aware that refrigerated trailer units are designed to remove any increased heat from product respiration, keep product temperatures stable, and control humidity by condensing the moisture that in the air. There are three integral parts of the refrigerated trailer system that aid in its functionality:

  • The Compressor – in a reefer unit, the compressor is driven by a small engine. The compressor draws gaseous refrigerant in and compresses it. The pressure inside the compressor liquefies the gas, and the now-liquid refrigerant gives off heat to the body of the compressor, and ultimately to the air.
  • The Condenser – the liquid from the compressor is still relatively warm, so it is pumped into a condenser; the condenser is a heat exchanger. Warmth flows from the liquid to the walls of the tubing, to fins on the tubing. The fins present more surface area for cooling outside air drawn through the condenser by a fan. Similar to the way a radiator cools an engine!!
  • The Evaporator – The evaporator is located in the trailer. The refrigerant, having given up much of its heat in the condenser, has turned into a cool liquid under pressure. It now flows through a metering valve into the evaporator. The metering valve controls the amount of refrigerant released into the evaporator, acting like a throttle to control the amount of cooling. It also works to help maintain back pressure in the high-pressure part of the system, which runs from the compressor to the evaporator.
  • In the evaporator, the refrigerant rapidly expands, once again becoming a gas. As it does, it absorbs a great amount of heat from its surroundings. Those surroundings are finned coils, which help transfer heat from air flowing over the fins to the refrigerant. Air from inside the trailer is blown over the evaporator. The refrigerant gas, now under low pressure, is drawn back to the compressor where the cycle starts again.
  • The trailer air, now cooled by giving up some of its heat to the evaporator, circulates back into the trailer to keep the cargo cool.

As we continually reinforce, these parts (as with any component of a truck or trailer) require regular maintenance to ensure they operate as designed. Maintenance schedules depend on how often the unit is in operation, and it is best to check with the specific manufacturer’s recommendations. In order to operate as designed, the unit also needs to be inspected regularly to make sure air passages are free and clear of debris; this includes checking channels on the floor, and removing the forward bulkhead. Experts also recommend routinely checking the evaporator for any paper or scraps that may affect cooling.

Refrigerated Trailers – Part 1: How They Work was last modified: by