There are three primary components in a vehicle’s air conditioning system including the compressor, condenser, and evaporator. These parts are connected by tubes and hoses to form a continuous path with two distinct sections: a high-pressure side and a low-pressure side. In order to transfer heat from the vehicle’s interior to the outside air, a chemical refrigerant is circulated throughout the system. In theory, the A/C system accomplishes the same task as the engine’s cooling system, in that both absorb the heat from one area and release it to another (heat transfer). While coolant remains a liquid during the heat transfer process however, refrigerant repeatedly alternates between a liquid and a gas as it circulates throughout the air conditioning system.
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| Orifice tube air conditioning systems regulate refrigerant flow to the evaporator using a fixed metering device (orifice tube). | In an expansion valve air conditioning system, refrigerant flow to the evaporator varies according to the pressure in the suction line (evaporator outlet). This is detected by a sensing bulb mounted on the line, and relayed to the expansion valve via a capillary tube |
The Refrigerant Cycle
The refrigerant cycle involves a three-step process that includes pressurization, condensation, and vaporization. Starting at the compressor, let’s identify these steps as we trace the flow of refrigerant through the system. The refrigerant enters the compressor through the suction port as a low-pressure vapor. After squeezing this vapor into a confined area (pressurization), it is released through the compressor’s discharge port. By pressurizing the refrigerant, the compressor causes the refrigerant vapor to become much hotter than the outside air. This ensures that it will change to a liquid as the cycle enters the next phase.
Once pressurized, the compressor pumps the high-pressure refrigerant vapor to the condenser, which is located directly behind the grille in front of the radiator. As outside air is drawn over the condenser by the engine fan, or forced past it by the ram-air effect, the incoming air absorbs the heat contained in the high-pressure vapor. This causes the vapor to condense into a high-pressure liquid, completing the second phase of the process (condensation).
As the refrigerant leaves the condenser, it makes its way toward the evaporator, which is located within the air hadling case along with the blower. Before entering the evaporator, the refrigerant flows through a metering device. This results in a significant drop in pressure, allowing the refrigerant to vaporize at a lower temperature. This ensures that the refrigerant will absorb the maximum amount of heat as the blower forces warm air over the evaporator. At this point, the vaporization phase is complete, and the heat-laden vapor is drawn back into the compressor so the cycle can be repeated.
Since heat is removed from the air during the vaporization phase, the air exits the panel vents at a much lower temperature. This not only results in cool air, but dehumidified air as well. Remember, warm air has high moisture content. Consequently, when the warm air comes in contact with the cold evaporator, the moisture condenses on the evaporator surface and eventually drains onto the ground. This is why a puddle of water forms under the car after it has been shut off with the air conditioner on.