Certain goods to be transported must be kept at certain temperatures. This is done by a refrigeration machine, it is either driven by a generator or a Diesel powered generator set. The former functions in the same way as the generator of a combustion engine (picture 5 below), it's normally larger and provides alternating current.

A refrigeration machine on a trailer, container or a semi-trailer, is protected by 32 Ampere fuses and is supplied with 400V from the tractor or 690V from a built in power system, also e.g., during the journey on a container ship. In the case of a Diesel powered generator set, the combustion engine is directly connected with the refrigeration machine.

There are several areas where the refrigeration can be installed (see above pictures), above the drivers cabin, on the front-side, e.g., of a semi-trailer, flat on the roof or on the side or under the loading area. Because starting of the Diesel powered units outside on a semi-trailer, can produce a sudden and considerable noise, their noise emissions, depending on where they have been parked, are of great importance. Apart from that, there is also an 'outdoor-directive' issued by the manufacturer which has to be complied with.

Of course, the ventilated evaporator is positioned inside the cargo area and the also ventilated condenser, on the outside. In the case of separate cooling areas more than one evaporator is needed. As a refrigerant e.g., R410A (with a boiling-point of -50°C) is used. Although this has a higher greenhouse-potential than R134a (which has a boiling-point of -23°C), it can specifically transport more heat.

This is important when a comparison is made with the interior of a motor car, the 13 meter long semi-trailer has a gigantic volume which has to be cooled. When using R410A however, higher pressures are necessary. Therefore, in proportion to the targeted cooling performance, piping with a smaller cross-section can be used.

As a rule, an air-circulation arises through the air movement away from the evaporator at the top of the cargo area and towards it at the bottom of the area. For this to function, there must be free spaces in the cargo area also between the stacks of cases, right up to the ceiling and underneath the pallets as well. The temperatures of the various goods should also not vary too much.

To avoid too much warming up when the doors are opened, there is an insulating-curtain directly behind the doors. The influx of too much humidity must also be avoided because it makes more frequent defrosting by heating the interior necessary. Otherwise the regular servicing intervals take care of the checking of the seals, the functions, the low- and high pressure and the coolant reservoir or its possible impurity. 10/14