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Cơ bản Air Conditioning System Types and Components

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  1. bikerviet
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    There are many different complexities of Air Conditioning systems. A simple configuration in shown here.

    [​IMG]
    The following sections describe the most common components in the automotive air conditioning system.
    Compressors

    General
    There are various makes and types of compressors used in automotive air conditioning systems. The internal design could be Piston, Scroll, Wobble plate, Variable stroke or Vane. Regardless, all operate as the pump in the A/C system to keep the refrigerant and the lubricating oil circulating, and thus to increase the refrigerant pressure and thus temperature.
    [​IMG]
    Wobble Plate

    A reciprocating piston, fixed displacement compressor. The pistons are operated by a wobble plate which moves them backwards and forwards in the cylinders.
    As the front shaft turns the wobble plate angle changes, causing the pistons to move in and out, pulling refrigerant vapour in through the suction side, compressing it and discharging this high pressure vapour into the condenser.


    [​IMG]
    Scroll Type

    This compressor uses a unique design with two scrolls, one is fixed and the other is movable, both are inter-leaved. The movable spiral is able to Orbit or oscillate without actually fully rotating. The movable scroll is connected to the input shaft via a concentric bearing. As the movable spiral oscillates within the fixed spiral, a number of pocket are formed between the spirals. As these pockets decrease in size the refrigerant is squeezed, the pressure increases and is discharged through a reed valve at the discharge port in the rear section of the compressor.



    [​IMG]
    Rotary Vane

    Rotary vane compressors consist of a rotor with three or four vanes and a carefully shaped rotor housing. As the compressor shaft rotates, the vanes and housings form chambers.
    The refrigerant is drawn through the suction port into these chambers, which become smaller as the rotor turns. The discharge port is located at the point where the gas is fully compressed.
    The vanes are sealed against the rotor housing by centrifugal force and lubricating oil. The oil sump and oil pump are located on the discharge side, so that the high pressure forces oil through the oil pump and then onto the base of the vanes keeping them sealed against the rotor housing.

    Compressor Mount and Drive
    This consists of a bracket to mount the compressor to the engine, a belt idler pulley and a compressor drive belt. There are two possible drive belt arrangements.
    Multiple Belts - individual belts used to drive separate engine ancilliaries​
    Serpentine Belt - all engine ancilliaries driven by a single belt​
    [​IMG] [​IMG]


    [​IMG]
    Compressor Clutch

    The clutch is designed to connect the rotor pulley to the compressor input shaft when the field coil is energised. The clutch is used to transmit the power from the engine crankshaft to the compressor by means of a drive belt.
    When the clutch is not engaged the compressor shaft does not rotate and refrigerant does not circulate, the rotor pulley free wheels. The field coil is actually an electromagnet, once energised it draws the pressure plate towards it, locking the rotor pulley and the pressure plate together causing the compressor internals to turn, creating pressure and circulating refrigerant.

    Condensers
    The condenser funtion is to act as a heat exchanger and allow heat to flow from the hot refrigerant to the cooler outside air.
    Refrigerant entering the condenser will be a high pressure high temperature vapour. As the refrigerant vapour travels through the tubes of the condenser heat is given off to the cooler ambient air, the refrigerant vapour condenses and changes to a liquid state.
    At this point a large amount of heat is given off by the refrigerant. The refrigerent will now be a hot, high pressure liquid.
    Design Types
    Serpentine
    This type of condenser consists of one long tube which is coiled over and back on itself with cooling fins added in between the tubes.
    [​IMG] [​IMG] Parallel Flow
    This design is very similar to a cross flow radiator. Instead of the refrigerant travelling through one passage (like the serpentine type) it can now travel across numerous passages. This will give larger surface area for the cooler ambient air to contact.

    [​IMG]
    Condenser Electric Fan

    Most vehicles with air conditioning require an electrical fan to assist air flow, either pushing or pulling the air through the condenser, depending on which side of the condenser the fan is placed.
    Most modern vehicles now have smaller front grilles or bumper bar openings. This causes poor air flow conditions especially at idle when A/C performance is limited by the amount of air flow over the condenser.


    Evaporators
    Refrigerant enters the evaporator coil as a cold low pressure liquid. As this liquid passes through the evaporator coil, heat moves from the warm air blowing across the evaporator fins into cooler refrigerant. This air that has now been cooled is then ducted into the cabin via the blower motor.
    When there is enough heat to cause a change of state, a large amount of heat moves from the air to the refrigerant. This causes the refrigerant to change from a low pressure cold liquid into a cold vapour.
    As the warmer air blows across the evaporator fins, moisture contained in that air (humidity) will condense on the cooler evaporator fins. Condensed moisture then runs off through the drain tubes located at the underside of the evaporator case.
    [​IMG]
    Serpentine Evaporator
    Same design as the serpentine condenser but approximately five times deeper. [​IMG]
    Plate & Fin Laminated Evaporator
    Similar operation to the parallel flow condenser where the refrigerant has a multi flow pass creating a larger surface area.

    Thermal Expansion Valves
    Refrigerant flow to the evaporator must be controlled to obtain maximum cooling, by ensuring that complete evaporation of the liquid refrigerant takes place. This is accomplished by the thermal expansion valve.
    Thermal Expansion Valve - Closed Thermal Expansion Valve - Open [​IMG] [​IMG]

    Thermal Expansion Block Valves
    The block valve differs from the previously mentioned expansion valve in that it has four passages, although the basic operation is exactly the same.
    Thermal Expansion Block Valve - Closed Thermal Expansion Block Valve - Open [​IMG] [​IMG]

    [​IMG]
    Orifice Tube

    At the orifice tube the refrigerant is forced to flow through a fine restriction. This causes a pressure drop and a temperature drop in the refrigerant entering the evaporator.
    A fine gauze filter is located at the inlet and outlet sides of the orifice tube to filter any contaminants from passing on to the evaporator.



    [​IMG]
    Filter Drier Receiver

    The filter drier acts as a particle filter, refrigerant storage container and most importantly a moisture absorber.
    Moisture, temperature and refrigerant causes hydroflouric and hydrochloric acid. The silica gel beads (dessicant) located in the filter drier absorb small quantities of moisture thus preventing acid formation.


    [​IMG]
    Accumulator

    The function of the accumulator is to store refrigerant, filter particles, absorb moisture and separate vapourous refrigerant from liquid refrigerant.
    The normal process of the accumulator system works when refrigerant leaves the evaporator coil as a mixture of vapour and liquid. This liquid enters the accumulator and falls to the bottom. The vapour rises to the top and continues onto the compressor. The liquid refrigerant in the bottom of the accumulator gradually vapourises off. This vapour rises, then pulls into the compressor.

    [​IMG][​IMG]Hoses
    Modern refrigerant hoses now incorporate a nylon inner lining to help reduce normal refrigerant leakage that would naturally occur through the porosity of rubber hoses.



    [​IMG]Sensors
    There are numerous sensors employed in the modern climate control system. These are linked to an electronic control unit to help automated use of the A/C system. These sensors include Sunload and Ambient Air Temperature sensors.


    Air Mix Door
    Temperature control is carried out by operating the temperature mode control, normally cable operated and connected to a door housed in the heater case. This door is located above the heater core and in full cold position, completely covers the heater core. As more heat is required, the door is operated and moves away from the heater core and allows radiant heat to rise and mix with fresh or A/C air to increase the vent temperatures to the desired comfort level required.
    [​IMG][​IMG]

    Electronic Climate Control
    ECC systems operate with the same basic components as in the manually controlled systems, such as condenser, compressor, evaporator and heater. The major difference being that the ECC system can maintain a preset level of cooling or heating selected by the vehicles operator once the automatic mode is selected.
    Electronic sensoring devices allow the ECC to respond to various changes in sunload, interior cabin temperature and ambient temperature. The ECC system will adjust automatically to any temperature and climate changes, to keep the vehicle cabin interior within the pre-selected temperature range.
    This is accomplished by adjusting:
    [​IMG]
    • Blower fan speeds
    • Air mode positions
    • A/C activation
    • Heater tap activation
    • Air mix door movement
    • Fresh/Recirculation door positions
     
  2. vvn56
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