All refrigeration systems for transport are based on the same operating principle.

Exploiting the physical features of the refrigeration gas contained in the circuit, the refrigeration system absorbs the heat from inside the loading compartment through the evaporating unit and releases it outside through the condensing unit.
The thermal exchange takes place thanks to the circulation of the air, so it is essential to guarantee that this occur freely around the goods inside the loading compartment; inflow and outflow of the air from the evaporating unit must always be free from obstacles.
The thermostat is the refrigeration unit control device. The required temperature (setpoint) is programmed on the thermostat, in relation to the transported product.
The refrigeration system works until the setpoint is reached and then it stops. The system starts up again automatically when the temperature inside rises 3°C above the setpoint.

Important: setting the thermostat to a lower temperature than the one required does not increase the cooling capacity and does not speed up the time necessary to cool the loading compartment to the setpoint. The system works at maximum power, regardless of the temperature set.

The refrigeration systems for transport are mechanical machines which require appropriate regular maintenance to guarantee optimal operation. While they are designed to operate on a vehicle, the systems are subject to the most varied climatic conditions, heat, vibrations, dirt and other things that might prevent their correct operation every day.
Any system must be taken regularly to an authorised service centre for servicing; the frequency of this servicing depends on the model and is indicated in the maintenance manual supplied with the system.
The user must also carry out some simple checks to guarantee the correct operation and durability of the system. Here is a list of helpful suggestions.

• Regularly check the conditions of the condensing unit heat exchanger (the external component of the refrigeration unit).Dirt, insects and other materials can block the passage of the air through the core fin and prevent the system from releasing the heat into the environment.Regularly clean the exchanger core with an air compressor, paying specific attention not to bend the aluminium fins. Never use a steam or hot water cleaner.
• Detergents for washing the vehicle are corrosive and, as time goes by, can damage the copper components inside the refrigeration unit. Avoid using these products to clean the condensing unit to prevent the formation of gas leaks.
• Regularly check the tension and wear and tear of the belts on the compressor installed on the vehicle engine (in models with driven compressor). Do not leave the system switched off for long periods of time (2-3 months). Even if it is not necessary to use the system because the outside temperature is low, switch on the refrigeration unit for five minutes at least once a month. The circulation of the gas and oil contained in it prevents the seals from drying out, eliminating the risk of leakage.
• If you hear strange noises, contact your service centre to have the unit checked. If you take prompt action, little things like the loosening of a bolt or a belt are inexpensive to put right.If, on the other hand, you wait too long, you can run into more serious problems like the snapping of a belt or the breakage of the compressor brackets or something else.
• Correct and regular maintenance makes it possible to obtain compensation for damages due to breakage or malfunction of the refrigeration unit from the insurance company. Vehicle liability policies contemplate an obligation to present invoices for the servicing of the refrigeration system.

The basic principle that regulates refrigerated transport is that the refrigeration systems for this purpose are conceived to conserve the temperature of the product, not to reduce it.
This means that the product has to be loaded only when the temperature has been reduced to an appropriate value using suitable refrigeration cells.
If this does not happen the product will reach the required temperature only after several hours, even days, depending on the type of product and the temperature concerned. When a product is cooled, it is its water content that cools, so goods with a high water content (e.g.: milk, mozzarella, meat) require more cooling power than others.
Pre-cooling of the insulated vehicle or cell.
The empty loading compartment of a van or the cell of a lorry parked in the sun absorb heat from the outside.
The heat produced by the sun's rays, ground and air is absorbed through the walls and transmitted to the air inside the loading compartment and is known as residual heat. The insulation panels do not eliminate the transmission of heat, they only slow it down; in addition, the insulating material absorbs part of this thermal energy like a sponge.
This is why it is essential to pre-cool the vehicle before loading the goods.
Switch on the refrigerator for at least 30 minutes keeping the doors closed; when the temperature of the air inside the loading compartment reaches the required temperature, it is necessary to wait another 10-15 minutes to allow the insulated walls to disperse the heat accumulated earlier.
Only after carrying out this procedure should you switch off the refrigeration system and load the goods.

Loading and unloading the goods.
During all the loading and unloading procedures, it is recommended to keep the doors open only for the duration necessary for the operation. The refrigerator must also be switched off. These operations are necessary to prevent hot, humid air from entering the area under controlled temperature.
The number of times the doors are opened every day and the interval of time between each opening are of fundamental importance.
Every opening allows hot, humid air to enter the refrigerated compartment, causing the temperature to rise; if this happens frequently, it is advisable to fit curtains inside to limit this phenomenon.
Always leave a space of at least 25 cm between the load and the ceiling. Cold air from the evaporating unit must be able to circulate freely to the bottom of the refrigeration compartment. Air must also be able to circulate freely all around the product.

The exposure of chilled products to a temperature that is too low or too high can cause significant degradation of these products.
If the temperature is too high, for example, fruit and vegetables over ripen, wilt and suffer surface burns; if they are too low, even when above zero, the skins can split and the product can dehydrate. Bananas, for example, are one of the most sensitive fruits and suffer from this phenomenon at temperatures below +13°C.
During ripening fresh fruit and vegetables produce a certain amount of heat, known as breathing heat; constant air circulation is essential to eliminate this heat from the loading compartment.
Products frozenat -20°C suffer irreversible changes to their molecules if temperatures rise above -10°C, significantly altering the product quality.
Ice cream, for example, while remaining frozen, loses its softness and reduces in volume.