Air Conditioning: Evaporator

The evaporator is placed in the climate system's distribution housing. It is reached from the right-hand side of the distribution housing.

In the refrigerant circuit, the evaporator is located on the low pressure side between the expansion valve and the compressor.

The task of the evaporator is to cool and dry the air.

The refrigerant (the volume that is measured by the expansion valve) is sprayed into the evaporator. As soon as the refrigerant enters the cooling pipes, it evaporates due to the drop in pressure. During this process, heat is also extracted from the cooling pipes. The cooling pipes and the entire evaporator cool immediately. The refrigerant gas is then drawn out using the compressor.

When the hot air entering the passenger compartment encounters the cold evaporator, the humidity in the air condenses on the evaporator. The water drains out under the vehicle via a drain hose. In the event of high humidity, this may be considerable quantities of water, which is often mistaken for a water leak from the engine for example.

The heat (energy) released during condensing is transferred to the refrigerant which vaporizes, the temperature difference between the air and the refrigerant drops. High humidity therefore results in an increased cooling requirement.

The surface of the evaporator is polyurethane coated to reduce bad odors. The polyurethane coating reduces the surface tension of the water and makes it easier for the water to run off.

The evaporator consist of a tubular coil in which the refrigerant flows. The coils are equipped with flanges to increase the heat absorbing area. The evaporator is tilted to make it easier for the condensation water to drain off.

There is a low pressure in the evaporator on account of the restriction on the expansion valve and the compressor's suction effect.

To obtain sufficient cooling capacity, the refrigerant's evaporation temperature must be considerably lower than the temperature desired in the passenger compartment. But to prevent the moisture that has condensed on the evaporator from freezing to ice, the air is not cooled below approximately +3 °C (at which stage the temperature of the refrigerant in the evaporator is approximately -3 °C).

There is a temperature sensor after the evaporator. The temperature sensor detects the temperature of the air that has passed through the evaporator. When the temperature is too low, the compressor is switched off. This is to prevent ice forming on the evaporator.

It is important that there is the correct amount of refrigerant in the climate control system.

• Too much refrigerant in the evaporator causes the refrigerant to heat up, but it only evaporates partially. This means that a smaller amount of heat is absorbed from the air, which results in reduced cooling capacity
• Too little refrigerant in the evaporator causes the refrigerant to evaporate and the vapor to overheat. This means that a smaller amount of heat is absorbed from the air, which results in reduced cooling capacity.