The refrigeration principle of automobile air conditioner, like other refrigeration air conditioners, is the principle of absorbing a lot of heat energy when the refrigerant R- 134a changes from liquid to gas. The compressor of automobile air conditioner transmits power through the belt of automobile engine (non-independent air conditioner). The compressor sucks in low-temperature and low-pressure refrigerant gas, which is compressed into high-temperature and high-pressure gas, cooled by the condenser radiator pipe and turned into high-pressure and medium-temperature liquid. After dehumidifying and buffering by the liquid storage dryer, it flows to the expansion valve at a relatively stable pressure and flow rate, and finally flows to the evaporator after throttling and depressurizing. When the refrigerant encounters a low pressure environment, it will evaporate and absorb a lot of heat energy. The air in the carriage continuously flows through the evaporator, so the temperature in the carriage decreases. After the liquid refrigerant flows through the evaporator, it becomes low-pressure gas again and is sucked into the compressor again for the next cycle. In the whole system, the expansion valve is the mechanism to control the refrigerant to enter the evaporator. If too much refrigerant enters the evaporator, it will not evaporate easily, and too little cold air will not be enough. Therefore, the expansion valve is the adjustment center. The compressor is the heart of the system and the power source of system circulation.
Because the automobile air conditioner is a mobile vehicle air conditioner, its dynamic and rotating conditions are worse than those of the fixed air conditioning system. With the flutter of the car, the refrigerant in the air-conditioning system leaks more easily than that in the fixed one, and the air-conditioning system is maintained more frequently than that in the fixed one. When the air duct system in air conditioning sucks in fresh air, it often sucks in dust and blocks the filter screen and evaporator.
2. Classification of automobile air conditioning system (by power supply)
1. Independent air conditioner: There is a special power source (the second engine) to drive the compressor to run, which is generally used in buses. This is because the internal space of the bus is large, which requires higher operation effect of the air conditioner. Independent air conditioners need two engines and are limited to buses, which leads to high fuel consumption, high cost and difficult maintenance.
Dependent air conditioning: an air conditioning system that directly uses the automobile engine to run. The dependent air conditioner is driven by the main engine and controlled by the electromagnetic clutch. When the power supply is turned on, the clutch is disconnected and the compressor stops, so as to adjust the supply of cold air and achieve the purpose of controlling the temperature in the compartment. Its advantages are simple structure, convenient installation and arrangement and low noise. Because it needs to consume the power of the main engine 10%- 15%, it directly affects the acceleration performance and climbing ability of the car. At the same time, its refrigeration capacity is affected by the vehicle speed. If the car stops running, its air conditioning system will also stop running. Nevertheless, dependent air conditioners have become the leading products in the market because of their low cost (relatively independent air conditioners) and reliable quality. At present, most cars, vans and minibuses use this kind of air conditioner. Non-independent air conditioning at present.
Three. Composition of automobile air conditioner
Generally, automobile air conditioner is mainly composed of compressor, electric control clutch, condenser, evaporator, expansion valve, liquid storage dryer, hose, condensing fan, vacuum solenoid valve, idle machine and control system. Automobile air conditioners are divided into high-pressure pipelines and low-pressure pipelines. The high-pressure side comprises a compressor output side, a high-pressure pipeline, a condenser, a liquid storage dryer and a liquid pipeline; The low-pressure side includes evaporator, accumulator, air return pipe, compressor input side and compressor oil pool.
Compressor: the heart of air conditioning refrigeration system is the power source of circulating refrigerant in the system. Its function is to make the refrigerant complete the transformation process from gas to liquid, and achieve the purpose of cooling and condensing the refrigerant. At the same time, in the whole air conditioning system, the compressor is also the pressure source of the running medium in the pipeline. Without it, the system will not only not cool down, but also lose the power to run. The rotating shaft of the compressor is connected with the crankshaft of the engine through an electromagnetic clutch and a belt to obtain power. This is because when the sensor installed at the outlet of the evaporator senses that the temperature of the wind is not low enough, it will close the electromagnetic clutch of the compressor through a circuit, so that the compressor can run with the engine to realize refrigeration. When the air outlet temperature is lower than the set temperature, the electromagnetic clutch is controlled to cut off, so that the compressor does not work. If this control fails, the compressor will continue to work, causing the evaporator to freeze and the pipeline pressure to exceed the standard, eventually destroying the system and even causing damage.
Condenser and evaporator: both of them are devices covered with metal sheets on a row of winding pipes to dissipate heat, so as to realize the heat exchange between outside air and substances in the pipes. Condensation of condenser means that the refrigerant in the pipeline is cooled from gas to liquid, which is usually installed in the front of the car. Together with the water tank, it enjoys the cool breeze blowing from the front, which cools and condenses the condenser. Evaporator and condenser are just the opposite, and condenser is the place where refrigerant changes from liquid to gas (i.e. evaporation) to absorb heat.
Liquid storage dryer: a device that stores refrigerant and absorbs moisture and impurities in refrigerant. On the one hand, it is equivalent to the fuel tank of a car, which supplements the extra space for the leaked refrigerant. On the other hand, like an air cleaner, it filters out impurities doped in refrigerant. The liquid storage dryer is also equipped with a certain silica gel substance to absorb water.
Pipeline: Metal pipeline must be used, because a certain pressure of refrigerant should be injected. Especially from the compressor to the condenser to the refrigerant bottle and then to the expansion valve, because it belongs to the high pressure section of the system, the requirements for high pressure resistance are higher than other pipelines.