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An Introduction to Air Conditioning

An overview of air conditioning

Ivan W. Anderson

on 16 April 2013

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Transcript of An Introduction to Air Conditioning

An Introduction to
Air Conditioning The compressor intake stroke is also known as the suction stroke.

As the compressor operates, the maximum possible charge of refrigerant vapor has been drawn in at bottom dead center of the compressor piston’s suction stroke.

When the piston begins its discharge stroke, the pressure increases, shutting the suction valve and opening the discharge valve at the same time.

The charge of refrigerant vapor is pushed out of the compressor into the high-side refrigerant line and travels toward the condenser.

The refrigerant vapor is compressed simultaneously throughout the entire high side of the air-conditioning system. The desiccant is classified as XH-5 for CFC-12 systems and XH-7 or XH-9 for HFC-134a systems. The desiccant used on a CFC-12 system is not compatible with HFC-134a systems.

The desiccant (accumulator or receiver-drier) should also be replaced on any air-conditioning system that has been left open to the atmosphere for any length of time (over 24 hours) or whenever the system has been left in a discharged condition.
The evaporator serves the same function for both the orifice-tube and the expansion valve–type air-conditioning system, and that is to allow the liquid refrigerant to evaporate and absorb heat from the passenger compartment. A typical accumulator used on a cycling clutch orifice-tube (CCOT) system. A receiver-drier, used on air-conditioning systems with an expansion valve, is located between condenser and evaporator.

This section of the air-conditioning system contains high-pressure liquid refrigerant. The receiver provides temporary storage for liquid refrigerant and includes a debris filter and a desiccant to remove moisture. Many receiver-driers contain a sight glass that provides a view of the liquid refrigerant in the system.

A drier is needed to remove moisture from the system. The drier contains a desiccant (silica alumina or silica gel), a drying agent that absorbs any moisture (water) in the air-conditioning refrigerant system. Moisture can combine with refrigerant to form an acid. Water can also freeze and form ice in the system. RECEIVER-DRIER The condenser serves the same function for both the orifice-tube and the expansion valve–type air-conditioning system, and that is to remove the heat from the refrigerant and cause the hot refrigerant vapors to condense into a hot liquid. The high-pressure gas changes (condenses) to form a high-pressure liquid as the heat from the refrigerant is released to the air. The condenser changes the refrigerant vapor into a liquid by transferring heat from the refrigerant to the air stream that flows between the condenser fins. This high-pressure gas flows into the condenser located in front of the cooling system radiator. The condenser looks like another radiator, with the same purpose and function—heat removal. All automotive air-conditioning systems are closed and sealed. A refrigerant is circulated through the system by a compressor that
is powered by the engine through an accessory drive belt.

Older systems used refrigerant CFC-12, commonly referred to by
its Dupont trade name of Freon® or R-12. Manufacturers now use HFC-134a, less harmful to the atmosphere.

The basic principle of the refrigeration cycle is that as a liquid changes into a gas, heat is absorbed. The heat absorbed by an automotive air-conditioning system is heat from inside the vehicle. AIR-CONDITIONING REFRIGERATION CYCLE Raises temperature of the gas so there is a temperature difference between outside (ambient) air and refrigerant in the condenser

Acts as the pump used to circulate refrigerant through the system

Often switches on and off (cycles) to control evaporator temperatures

Is the major reason why there is refrigerant oil in the system. Oil in the refrigerant lubricates the moving parts of the compressor. The air-conditioning compressor is driven by the engine with an accessory drive belt. A magnetic clutch is usually used to connect and disconnect the drive pulley to the compressor as needed for cooling or defrosting. The compressor: COMPRESSORS The condenser looks like a cooling system radiator, because it is designed to radiate heat from the refrigerant to the outside air.

When refrigerant leaves the compressor it is over 300°F (150°C) as it enters the condenser. Even on a hot 100°F (38°C) day, there is a difference in temperature between the outside air and the refrigerant inside the condenser. Heat always travels hot to cold.

Heat in the hot refrigerant radiates into the outside air. As heat travels into the air, high-pressure gas refrigerant changes state and becomes high-pressure liquid. The condenser condenses refrigerant from a gas (vapor) to a liquid.
CONDENSER The high-pressure liquid then flows through a device that meters the flow into the evaporator. When the high pressure of the liquid drops, it causes the refrigerant to vaporize.

Air is blown through the evaporator by the blower motor and is cooled as heat is removed from the air and transferred to the refrigerant in the evaporator. How Does the Inside of the Vehicle Get Cooled?

The underlying principle involved in air-conditioning or refrigeration is that “cold attracts heat.” Therefore, a cool evaporator attracts the hot air inside the vehicle. Heat always travels toward cold and when the hot air passes through the cold evaporator, the heat is absorbed by the cold evaporator, which lowers the temperature of the air. Cooled air is then forced into the passenger compartment by the blower through the air-conditioning vents. The low-pressure refrigerant gas is
compressed into a
high-pressure gas
and forces the
refrigerant through
the system. The compressor provides the mechanical force needed to pressurize the refrigerant. After the refrigerant has evaporated into a low-pressure gas in the evaporator, it flows into the engine-driven compressor. Continued Liquid refrigerant evaporates in a small radiator-type unit called the evaporator. As the refrigerant evaporates, it absorbs heat as it changes from a liquid to a gas. As heat is absorbed by the refrigerant, the evaporator becomes cold. Automotive air-conditioning function in this manner: NOTE: A liquid cannot be compressed. If liquid refrigerant were to enter
the compressor, the compressor would lock up and be damaged. Preventing liquid refrigerant from reaching the compressor
Holding a reserve of refrigerant
Holding the desiccant (helping remove moisture) An accumulator, used on systems with an orifice tube, is located between evaporator and compressor. Refrigerant in this section of the cycle is a low-pressure gas. The purposes of the accumulator: ACCUMULATOR The evaporator transfers heat from the air to refrigerant flowing through it. Heat from the air causes low-pressure liquid inside the evaporator to evaporate into low-pressure gas. As the refrigerant changes state, it absorbs heat. A blower motor with a squirrel cage fan circulates air through the evaporator and forces the cooler air into the passenger compartment. NOTE: If the carpet or floor of the vehicle is wet on the passenger side, the cause is often a clogged evaporator drain hose. The opening, called the
condensate line, is frequently clogged with mud, debris, or leaves. To check the drain opening, hoist the vehicle and insert a wire or screwdriver into the end of the hose opening at the bottom of the evaporator housing. The evaporator looks like a small radiator located in a housing on the passenger side of the bulkhead (firewall). EVAPORATOR What happens? not used Used instead clutch coil pulley
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