How to Use Internal and External Circulation in Automobile Air Conditioning Techniques Analysis

Nowadays, every passenger car that leaves the factory is equipped with an air conditioning system to meet the comfort of driving in hot and cold environments. In order to meet the needs of different environmental temperatures and air quality, the air conditioning system provides two working modes: internal circulation and external circulation. The function of the external circulation is to supplement fresh air, while the function of the internal circulation is to timely and effectively prevent external dust and harmful gases from entering the car, such as blocking harmful exhaust emissions from the front car during driving through smoke, dust, odor areas, or dense and compact driving of vehicles.

Car air conditioners are similar in structure to ordinary household air conditioners, including compressors, condensers, evaporators, expansion valves, drying reservoirs, and pipelines. When the user opens the A/C switch, the engine drives the compressor to start working, driving the refrigerant to circulate in the sealed air conditioning system. The compressor compresses the gaseous refrigerant into high-temperature and high-pressure refrigerant gas and then discharges it from the compressor.

After the high-temperature and high-pressure refrigerant gas flows into the condenser through the pipeline, it dissipates heat and cools down inside the condenser, and condenses into a high-temperature and high-pressure liquid refrigerant to flow out. The high-temperature and high-pressure liquid refrigerant enters the drying reservoir through a pipeline, and after drying and filtering, flows into the expansion valve. The high-temperature and high-pressure liquid refrigerant undergoes a rapid change in state after being throttled by an expansion valve, becoming a low-temperature and low-pressure liquid refrigerant.

The low-temperature and low-pressure liquid refrigerant immediately enters the evaporator, absorbing the heat of the air flowing through the evaporator, reducing the air temperature, blowing out cold air, and producing a refrigeration effect. The refrigerant itself evaporates into a low-temperature and low-pressure gaseous refrigerant due to the absorption of heat. The low-temperature and low-pressure gaseous refrigerant is sucked in by the compressor through the pipeline, compressed, and enters the next cycle. As long as the compressor continues to work, the refrigerant continues to circulate in the air conditioning system, producing a cooling effect; When the compressor stops working, the refrigerant in the air conditioning system stops flowing and does not produce a cooling effect.

It is worth noting that the car air conditioning does not provide a heating mode. In winter, when the temperature inside the car is low, the heating switch can be turned on, and the heated air can enter the cabin through the engine coolant cooling system to heat the cabin.

The internal and external circulation is controlled by a conversion switch. Nowadays, cars support three modes of setting: automatic, internal circulation, and external circulation. The automatic mode is mainly internal circulation, and the external circulation is enabled through the timely conversion switch control of the air conditioning sensor to ensure that the air quality in the car does not experience a decrease in air quality (oxygen content decreases, pollution intensifies) and other conditions.

As the name suggests, the internal and external circulation of the car's air conditioning system cools and circulates the air inside the carriage. At this time, the air inlet of the blower is turned off, and the exhaust outlet at the rear of the carriage is also turned off. Due to isolation from the outside, the oxygen content in the air gradually decreases with the breathing of the passengers inside the carriage. Therefore, the internal circulation of the car cannot be turned on for a long time. If manual mode is selected, It is necessary to regularly start the external circulation to update the air quality inside the carriage.

The external circulation refers to the process in which the car air conditioner uses a blower to cool the external air into the carriage, and then it is discharged through the exhaust outlet at the rear of the carriage. Obviously, the external circulation always needs to cool the external air at maximum power, which will consume a lot of engine power. Additionally, although the car air conditioner is equipped with a filter element, the filter element cannot filter out car exhaust and toxic gases outside the carriage, So in these situations, it is necessary to activate internal circulation to ensure the air quality inside the carriage.

1. When using car air conditioners, it is necessary to regularly clean/replace the air conditioning filter element. If conditions permit, the air duct of the air conditioner can also be cleaned. In addition, for the current severe PM2.5 pollution, users can also use PM2.5 high-efficiency air filters to improve the driving environment.

2. Timely check if the air inlet is blocked. Leaves, shopping bags, and other items usually fall everywhere. If they happen to fall at the external air inlet of the air conditioner, they may be sucked into the external air inlet of the air conditioner. If left uncleaned for a long time, the fallen leaves will rot and spoil, polluting the air conditioning filter and producing a foul odor.

3. The opening of the car air conditioning requires certain temperature conditions, and the refrigeration system must ensure that the external temperature is not lower than 10 ℃, otherwise the air conditioning system cannot work. Of course, when the external temperature is lower than 10 ℃, there is indeed no need to use cold air to cool the cabin.

4. Do not keep the air conditioning set to internal circulation. Although internal circulation helps to save fuel, over time, the air inside the carriage may become turbid or even lack oxygen.

5. During both internal and external circulation, do not smoke inside the car. If smoking is necessary, it is necessary to open the window glass for a certain amount of air raid to allow smoke to spread out.

6. Try not to turn on the air conditioning to rest while parking. Due to incomplete combustion of gasoline in the cylinder, high concentrations of carbon monoxide are generated during parking, which can lead to poisoning or even death. During the driving process of a car, due to the convection of air through the air conditioning equipment, the concentration of carbon monoxide in the car with air conditioning is very low.