Air Conditioning Structure
Commercial vehicle air conditioners mainly have three major components, compressor, condenser, and evaporator. There are also a number of ancillary components, including expansion valves, liquid storage dryers, pipes, condensing fans, blowers, temperature sensing packages, etc.
●Function of main components
1. Compressor
Driven by the engine through a belt, its function is to inhale low-temperature and low-pressure refrigerant vapor, compress it to the required pressure, and then send it to the condenser. It is the power source of the entire air-conditioning refrigerant cycle. The higher the engine speed, the faster the refrigerant circulates and the greater the refrigeration power.
2. Condenser
Its function is to transfer the heat of high-temperature and high-pressure gaseous refrigerant to the outside air, causing the refrigerant to condense into liquid.
The condensation effect of the condenser on the refrigerant directly determines the cooling efficiency of the air conditioner.
There are usually three major ways to improve the condensation effect:
2.1. Increase the flow of air through the condenser.
2.2. Reduce the temperature of the air passing through the condenser.
2.3. Keep the condenser surface clean and free of contamination.
3. Evaporator
Usually arranged in the cab, its function is to absorb heat from the cab, so that the liquid refrigerant absorbs heat and vaporizes into gas.
4. Liquid storage dryer
The main function in the air conditioning system is to filter, dry, dehumidify and store excess refrigerant.
5. Expansion valve and temperature sensor package
Generally installed on the evaporator, the temperature sensing package is usually located at the evaporator outlet to detect the evaporator outlet temperature, automatically adjust the opening of the expansion valve, control the flow rate of the refrigerant, and control the stability of the temperature in the cab.
●Basic principles of refrigeration
In daily life, we all have this experience: when alcohol is used in the body, there will be a cold feeling. This means that when a liquid turns into a gas it absorbs heat, thus lowering its temperature. Automotive air conditioning refrigeration uses this basic principle. There are three main points:
1. When a liquid turns into a gas, it needs to absorb a lot of heat. The heat is absorbed and the temperature decreases.
2. The change in temperature is not only related to the amount of heat contained in the object, but also related to the volume and mass of the object.
3. The natural transfer of heat can only be from high-temperature objects to low-temperature objects. If we want to radiate heat from the car compartment at 25°C to the outside of the car at 35°C, we must rely on mechanical equipment and power consumption. These equipment and related accessories constitute the automobile air conditioning and refrigeration device.
The automobile air conditioning system uses the refrigerant to absorb the heat of the air in the vehicle room when it evaporates in the device, thereby reducing the air temperature and achieving cooling purposes.
A general refrigeration device is mainly composed of a compressor, condenser, expansion valve, evaporator and connecting pipelines. It has realized four basic cycles of compression, condensation, pressure reduction and throttling, and evaporation.
Compression process:
After starting the car's air conditioning system, the compressor starts working with the engine running, driving the refrigerant to circulate in the sealed air conditioning system. The compressor compresses the low-temperature and low-pressure gaseous refrigerant flowing back from the evaporator into high-temperature and high-pressure gas and discharges it from the compressor.
Condensation process:
The high-temperature and high-pressure agent gas enters the condenser through the pipeline, dissipates heat in the condenser, reduces the temperature, condenses into liquid agent gas, flows out of the condenser, and enters the dryer. After drying and filtration, it flows along the pipeline in a liquid state.
Throttling process:
The temperature of the high-pressure liquid refrigerant before entering the expansion is high. The refrigerant in this state undergoes throttling expansion in the expansion valve, the pressure drops, and it evaporates into a gaseous state.
Evaporation process:
When the refrigerant evaporates into a gaseous state, it needs to absorb a large amount of the temperature of the air flowing through the evaporator surface in the car, thereby lowering the temperature and achieving the purpose of cooling. The agent in the evaporator is completely evaporated, the temperature rises, and the machine continues to operate.
At the same time, when the hot and humid air encounters the cold fins on the back of the evaporator surface, it condenses into water and is discharged from the evaporator to the outside of the car.
