Air conditioning: Evaporator
The evaporator is an air heated heat exchanger located in the distribution housing for the climate control system.
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 consists of pipe loops in which the refrigerant flows. The loops have flanges to increase the heat absorbing surface. The evaporator is inclined to make it easier for the condensation to run off. 10 - 11 liters of condensation are formed per hour. The condensation is led via a drainage house out of the distribution housing and down under the vehicle.
If one experiences bad odors when the vehicle is started, a workshop can activate a function which starts the blower fan a moment after the ignition key is moved to the 0 position. The fan blows the evaporator dry for a few minutes to prevent condensation and bad odors the next time the vehicle is used.
In the refrigerant circuit, the evaporator is located on the low pressure side between the expansion valve and the compressor.
In the evaporator there is a low pressure due to the expansion valve choke and the suction effect of the compressor. When the refrigerant enters the evaporator via the expansion valve, it expands and both its pressure and temperature lower.
When the warm air encounters the cold evaporator, the humidity condenses on the evaporator. The heat (energy) that is released during condensation is transferred to the refrigerant which evaporates. The temperature difference between the air and the refrigerant reduces. High humidity results in an increased need for cooling.
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.