COOLING UNIT CONSTRUCTION/OPERATION
id071100101700
• The cooling unit consists of an evaporator, expansion valve, high pressure pipe, cooler case and thermistor.
• The cooling unit cools and dehumidifies the airflow from the blower unit.
• The thermistor is built into the cooling unit and controls the A/C compressor.
L.H.D.
R.H.D.
Evaporator
• The evaporator vaporizes the refrigerant flowing inside it. The latent heat of the vaporized refrigerant cools the air passing through the evaporator. At the same time, moisture in the air condensates. In this way, dehumidified air is supplied to the passenger compartment.
• The evaporator is a single tank drawn cup type. Because refrigerant flows through several separate tubes, flow path resistance is kept low and the surface area for heat exchange is increased, improving air conditioning efficiency.
Expansion Valve
• The expansion valve causes a sudden decrease in the pressure of the liquid refrigerant. This atomizes the refrigerant, making it easier for the evaporator to vaporize it. The expansion valve also regulates the flow volume of the refrigerant sent to the evaporator.
• The amount of refrigerant delivered to the evaporator is adjusted by the opening angle of the ball valve in the expansion valve.
• Opening angle is adjusted by a balance of the R-134a pressure (Pd) in the diaphragm, and a composite force of evaporator discharge pressure (PI) against the lower part of the diaphragm and spring force (Fs) pushing up the ball valve. When PI increases, the temperature of the temperature sensor near the diaphragm rises and the Pd heated by the R-134a in the diaphragm increases. When the Pd increases more than PI + Fs, the diaphragm is pushed down, and the shaft attached to end of the temperature sensor rod pushes down the ball valve, increasing the amount of liquid refrigerant flow. When the evaporator discharge refrigerant temperature decreases, PI + Fs increases more than Pd, the ball valve is pushed up, and the amount of liquid refrigerant flow decreases.