A/C Evaporators Function
The evaporator is tasked with removing heat and humidity from the passengers compartment. It is located in a plastic housing, typically a heating/cooling unit. The evaporator is a heat exchanger consisting of aluminum tubes and fins. A metering device controls the temperature of the evaporator by controlling the flow of liquid refrigerant. A decrease in pressure from the metering device causes a decrease in temperature in the evaporator core.
Refrigerant enters the evaporator from the bottom inlet tube as low pressure liquid. As it passes through the core toward the top it starts absorbing heat. Warm air from the passengers compartment cools as it passes through the evaporators fins and tubes.
Refrigerant has a very low boiling point. As it absorbs heat from the cabin it changes its state from a liquid to a vapor. This heat exchange causes the refrigerant to boil and expand. This expansion phase is why the outlet tube is larger than the inlet.
An evaporator is also a dehumidifier. As cabin air passes through the evaporator heat is removed leaving water molecules to form on its surface. The more humidity in the air the more condensation occurs. This moisture is collected in the base of the case and funneled outside of the vehicle through a drip tube.
