research air conditioning system and design teaching model

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MINISTRY OF EDUCATION AND TRAINING

<b>HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING </b>

<b> </b>

<b>GRADUATION PROJECT AUTOMOTIVE ENGINEERNG</b>

<b>RESEARCH AIR CONDITIONING SYSTEM AND DESIGN TEACHING MODEL </b>

<b>LECTURER: VU DINH HUAN</b>

<b>STUDENT: NGUYEN CONG KHANH NGUYEN MINH TRIET</b>

<small>S K L 0 1 2 5 5 3</small>

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<b>Major: AUTOMOTIVE ENGINEERING TECHNOLOGY Supervisor: MS. VU DINH HUAN. </b>

<b>Ho Chi Minh City, January 2024</b>

<b>RESEARCH AIR CONDITIONING SYSTEM AND DESIGN TEACHING MODEL</b>

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vii <small>THE SOCIALIST REPUBLIC OF VIETNAM </small>

<b>Independence – Freedom– Happiness </b>

<b>---EVALUATION SHEET OF DEFENSE COMMITTEE MEMBER </b>

Student name: Nguyen Cong Khanh Student ID: 19145191 Student name: Nguyen Minh Triet Student ID: 19145052 Student name: ... Student ID: ...

Major: Automotive Engineering Technology Project title: Research air conditioning system and design teaching model Name of Defense Committee Member: ...

<b>EVALUATION </b>1. Content and workload of the project ...

...

...

...

2. Strengths: ...

...

...

3. Weaknesses: ...

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<b>Acknowledgements </b>

Firstly, the team would like to express our sincere gratitude and deep appreciation to all the teachers of the Automotive Engineering Technology department, Faculty of Vehicle and Energy Engineering department, Ho Chi Minh city University of Technology and Education, who have cared for and taught us valuable knowledge and lessons so that the team could complete this project.

In particular, we would like to extend our thanks to our supervisor, Master Vu Dinh Huan, who directly guided us, patiently instructed us, and imparted practical knowledge and skills for us throughout the implementation of the project.

At the same time, we would like to thank thesis advisor, Doctor Le Thanh Phuc for taking the time to read the graduation thesis and for giving us valuable comments and suggestions to help improve our thesis.

Finally, We would like to thank our families and friends in the 19145CLA class, who have always accompanied, helped, and encouraged us so that we could complete the project in the best way.

We sincerely thank you.

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<b>List Of Figures </b>

Figure.2.1. Dashboard installed HVAC system ... 18

Figure.2.2. Boot installed single zone HVAC system ... 18

Figure.2.3. Dual zone dashboard installed HVAC system ... 19

Figure.2.4. Manual air conditioner ... 19

Figure.2.5. Automatic air conditioner ... 20

Figure.2.6. Air heating system ... 20

Figure.2.7. Air cooling system ... 21

Figure.2.8. Positive and negative pressure across the surface of the vehicle ... 22

Figure.2.9. (a) Fresh air inlet; (b) Fresh air inlet Ford Fiesta ... 23

Figure.2.10. Air filter ... 23

Figure.2.11. Air conditioning system ... 24

Figure.2.12. Structure of Through-Vane compressors ... 26

Figure.2.13. Working principle of Through-Vane compressors ... 27

Figure.2.14. Structure of Variable Type Compressor ... 27

Figure.2.15. Working priciple of Variable Type Compressor ... 28

Figure.2.16. structure of scroll compressor ... 29

Figure.2.17. Working principle of scroll compressor ... 29

Figure.2.18. Structure of Swash Plate Type (Fixed Displacement) ... 30

Figure.2.19.Operation of Swash Plate Type ... 30

Figure.2.20. Structure of magnetic clutch ... 32

Figure.2.21. Working principle of magnetic clutch ... 33

Figure.2.22. Condenser ... 34

Figure.2.23. Structure of condenser ... 35

Figure.2.24. Construction of multiflow subcool condenser ... 36

Figure .2.25. Structure of dryer ... 37

Figure.2.26. Structure of the block -type expansion valve ... 39

Figure.2.27. Operation of the block -type expansion valve ... 40

Figure.2.28. Structure of Thermal Expansion Valve ... 41

Figure.2.29. Serpentine Type ... 42

Figure.2.30. Drawn Cup Type... 42

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Figure.2.31. Structure of evaporator ... 43

Figure.2.32. Sight glass: (a) clear; (b) foamy; (c) streaky; (d) cloudy ... 44

Figure.2.33. Condenser Fan ... 45

Figure.2.34. Blower motor ... 46

Figure.2.35. The Electronic Automatic Temperature Control (EATC) system ... 48

Figure.2.36. : The automatic air conditioning system... 49

Figure.2.37.The automatic air conditioning system consists of several components ... 50

Figure.2.38. ECU control A/C ... 51

Figure.2.39. Room temperature sensor ... 52

Figure.2.40. Ambient temperature sensor ... 52

Figure.2.41. Solar sensor ... 53

Figure.2.42.Evaporator temperature sensor ... 53

Figure.2.43.Water temperature sensor ... 54

Figure.2.44. Position of air mixing motor ... 54

Figure.2.45.working principle of air mixing motor ... 55

Figure.2.46. Position of air inlet motor ... 56

Figure.2.47. Operation of air inlet motor ... 56

Figure.2.48. Position of air vent mode servo motor... 57

Figure.2.49. Operation of air vent mode servo motor ... 57

Figure2.50. Control the outlet air temperature (TAO) ... 58

Figure.2.51. Logo Arduino... 59

Figure.2.52.Arduino Uno R3 ... 60

Figure.2.53. I2C Serial Interface 20x4 LCD Module ... 62

Figure.2.54. R134a Pressure-Temperature chart ... 63

Figure2.55. LCD display to Arduino wiring ... 64

Figure.2.56. DC-DC 3A LM2596 low-voltage power ... 64

Figure.2.57. Coolant Temperature Sensor for Kia Sportage 95-97 K857418840 ... 65

Figure.2.58. Steinhart and Hart Equation 1 ... 66

Figure.2.59. Steinhart and Hart Equation 2-4 ... 66

Figure.2.60. Solving the Steinhart and Hart Equation for Coefficients ... 67

Figure.2.61. Sensor raw data vs Steinhart and Hart Equation Chart ... 67

Figure.2.62. G1/4 pressure transducer sensor ... 68

Figure.2.63. Pressure value of the model in compared with pressure gauge ... 70

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<b>Figure.3.1. Autodesk Inventor Professional ... 71 </b>

Figure.3.2. Inventor Professional sketch interface ... 72

Figure.3.3. The model framework designed in Inventor Professional ... 73

Figure.3.4. 2D design of the model frame ... 73

Figure.3.5. Designing Electrical Panel with AutoCAD ... 75

Figure.3.6. Front of the heater control ... 75

Figure.3.7. Back of the heater control ... 76

Figure 3.8.Electrical circuit diagram of the Lexus ES300 1996 air conditioning system . 79 Figure 3.9.Electrical circuit diagram of the Lexus ES300 1996 air conditioning system . 80 Figure 3.10. Heater control buttons ... 81

Figure 3.11. FACE mode ... 82

Figure 3.12. BI-LEVEL mode ... 82

Figure 3.13. FOOT mode ... 83

Figure 3.14. FOOT/ DEF mode ... 83

Figure 3.15. Complete Model (Front) ... 85

Figure 3.16. Complete Model (side) ... 86

Figure 3.17. Complete Model (back) ... 86

Figure 3.18. FACE mode ... 88

Figure 3.19. FOOT mode ... 89

Figure 3.20.BI-LEVEL mode ... 89

Figure 3.21. FOOT/DEFROST (F/D) mode ... 89

Figure 3.22. RECIRCULATION mode ... 90

Figure 3.23. FRESH AIR mode ... 90

Figure 3.24.Display pressure value at MAX COLD temperature level ... 91

Figure 3.25. Display pressure value at 25^oC temperature level ... 91

Figure 3.26. Display pressure value at MAX HOT temperature level ... 91

Figure.4.1.Connecting compressors and meters to the model. ... 93

Figure.4.2. Simulate the vacuum process ... 94

Figure.4.3. Maintain the status for 5-10 minutes to check for leaks. ... 94

Figure.4.4. Press the air vent at the yellow hose of the gauge set to release the remaining air inside the hose ... 95

Figure.4.5. Simulate the gas charging process from the high pressure side ... 96

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Figure.4.7. pressure value when system working normally ... 98

Figure.4.8. pressure value when leaking ... 99

Figure.4.9. Pressure value when the system lacks gas ... 100

Figure.4.10. Pressure value when the system has poor cooling ... 100

Figure.4.11. Pressure value when the system having the broken compressor, the dryer is off ... 101

Figure.4.12. Pressure value when the system is blocked by the expansion valve ... 102

Figure.4.13. Circuit diagram of air mix servo motor ... 105

Figure.4.14. Supply power to the air mixing motor ... 105

Figure.4.15. Circuit diagram of air inlet servo motor ... 106

Figure.4.16. Supply power to the air mixing motor ... 107

Figure.4.17. Supply power to the air vent mode control servo motor ... 107

Figure.4.18. Solar Sensor ... 109

Figure.4.19. Circuit diagram of Solar Sensor ... 109

Figure.4.20. Evaporator temperature sensor ... 110

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<b>List Of Tables </b>

Table.2.1. Arduino Uno R3 Specification ... 60

Table.2.2. Specification of 20x4 LCD Module ... 62

Table.2.3. Saturation Pressure-Temperature Data for R134A ... 63

Table.2.4. specification of DC-DC 3A LM2596 ... 64

Table.2.5. Specification of Coolant Temperature Sensor ... 65

Table 2.6. Sensor raw data vs Steinhart and Hart Equation ... 67

Table.2.7. Specification of pressure sensor ... 68

Table.2.8. Pressure Data ... 69

Table.3.1. Symbols and Meanings of Jack Pins ... 76

Table.3.2. Main parts of the model ... 87

Table.4.1. The standard value measured between the pins ... 103

Table.4.2. The meaning of the pins on the servo motor of each wind direction modes .. 108

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<b>List Of Abbreviations </b>

LCD : Liquid Crystal Display

HVAC : heating, ventilation, and air conditioning

MPVs: Multi Passenger Vehicles

ECU: Electronic Control Unit

HI: High

LO: Low

MED: medium

NTC: Negative temperature coefficient

A/C: Air Conditioner

TXV: Thermostatic expansion valve

EATC: Electronic Automatic Temperature Control

MH: Max Hot

MC: Max Cool

TAO: Temperature Air Outlet

PWM: Pulse Width Modulation

I2C: Inter-Integrated Circuit

MIG: Metal Inert Gas

REC: Recirculation mode

FRS: Fresh air mode

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<b>Abstract </b>

As humans evolve and progress, their needs are continually advancing, and the use of cars is becoming more widespread. The demand for comfort and safety features in vehicles is also on the rise. Modern car amenities, such as music systems, movie players, smart systems (like anti-theft locks, automatic headlights, smart rearview mirrors, etc.), and particularly the car's air conditioning system, are evolving and playing a crucial role in meeting these needs.

Recognizing this trend, the Ho Chi Minh City University of Technology and Education has incorporated the study of automatic air conditioning systems into its curriculum. This includes comprehensive theoretical instruction and practical models that demonstrate the principles of operation and vehicle systems. Leveraging this knowledge, the group has chosen to focus on the topic: "Research Air Conditioning System And Design Teaching Model" based on 1996 Lexus ES300 . The primary objective is to conduct in-depth research on automatic air conditioning systems and to develop a complete model. The content expressed through 5 chapters:

Chapter 1 : Introduction

Chapter 2 : The Automatic Air Conditioning Control System

Chapter 3 : Design And Build The Air Conditioning System Model Chapter 4 : Practical Exercises Applying The Model

Chapter 5 : Conclusion

<i><b>Keyworks: Automatic Air Conditioning System, 1996 Lexus ES300 </b></i>

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<b>1.1.Reason For Choose Topic... 14</b>

<b>1.2.Purpose, scope of research: ... 14</b>

<b>1.2.1.Research purpose ... 14</b>

<b>1.2.2.Research scope ... 15</b>

<b>1.3.Research method ... 15</b>

<b>1.4.The scope of application ... 15</b>

<b>Chapter 2: THE AUTOMATIC AIR CONDITIONING CONTROL SYSTEM ... 16</b>

<b>2.1.Introduction about Air Conditioning ... 16</b>

<b>2.2.Overview of the air conditioning system ... 17</b>

<b>2.3.Overview of the automotive air conditioning system ... 18</b>

<b>2.3.1.Classification of air conditioning systems by zone [6] ... 18</b>

<b>2.3.2.Classification of air conditioning systems by control method ... 19</b>

<b>2.3.3.Temperature control ... 20</b>

<b>2.3.4.Air distribution through the interior of the vehicle ... 22</b>

<b>2.4.The structure and operation principle of a car air conditioning system ... 24</b>

<b>2.4.1.The general structure of a car air conditioning system ... 24</b>

<b>2.4.2.The car air conditioning system operator ... 24</b>

<b>2.5.Structure and operating principles of some main parts in the automatic air conditioning control system ... 25</b>

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<b>2.7.Overview of the air conditioning system in cars ... 48</b>

<b>2.7.1.The automatic air conditioning system consists of several components ... 50</b>

<b>2.8.Servo motors ... 54</b>

<b>2.8.1.Air mix control servo motor ... 54</b>

<b>2.8.2.Air inlet control servo motor... 55</b>

<b>2.8.3.Air vent mode control servo motor ... 57</b>

<b>2.8.4.Control the outlet air temperature (TAO) ... 58</b>

<b>2.9.Displays temperature and pressure at the condenser and evaporator ... 59</b>

<b>2.9.1.Introduction to Arduino ... 59</b>

<b>2.9.2.Introduction to Arduino Uno R3 ... 60</b>

<b>2.9.3.I2C Serial Interface 20x4 LCD Module ... 61</b>

<b>2.9.4.The temperature and pressure sensor. ... 65</b>

<b>Chapter 3: DESIGN AND BUILD THE AIR CONDITIONING SYSTEM MODEL ... 71</b>

<b>3.1. Mechanical Design ... 71</b>

<b>3.1.1. Autodesk Inventor Professional overview ... 71</b>

<b>3.1.2. Frame Design on Inventor Professional ... 72</b>

<b>3.2. Frame Construction and Part Search ... 73</b>

<b>3.2.1. Searching for Replacement Parts in the Car Air Conditioning System ... 74</b>

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<b>3.3.1. Restoring the Electrical Circuit of the Model ... 74</b>

<b>3.3.2. Designing Electrical Panel with AutoCAD ... 74</b>

<b>3.4. Completing the Electrical Construction of the Model ... 75</b>

<b>3.4.1. Heater Control ... 75</b>

<b>3.4.2. Electrical circuit diagram of air conditioning system ... 78</b>

<b>3.5. Completing the automatic air conditioning system model ... 81</b>

<b>3.5.1. Instructions for using the model, operating the model, safety precautions during operation ... 81</b>

<b>3.5.2. Result ... 85</b>

<b>Chapter 4: PRACTICAL EXERCISES APPLYING THE MODEL ... 93</b>

<b>4.1. Practical exercise on gas charging for the air conditioning system using R314a refrigerant ... 93</b>

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<b>4.3. Exercise of measuring the voltage of the air conditioning system ... 103</b>

<b>4.6.2. Perform a outside inspection and diagnosis ... 112</b>

<b>4.7. The process of diagnosing system errors of the model ... 113</b>

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<b>Chapter 1: INTRODUCTION 1.1. Reason For Choose Topic </b>

Through each stage of existence and development, human being needs are increasingly improving, cars are increasingly widely used. Users' requirements for comfort and safety features are also increasing. Modern car amenities are increasingly developing, playing an important role in ensuring customers' needs such as listening to music, watching movies, and some smart systems (anti-theft locks, automatically headlights, smart rearview mirror,...) and one of the must-have amenities in a car is the car's air conditioning system.

Ho Chi Minh City University of Technology and Education soon caught up with the trend, introduced the automotive air conditioning system into teaching based on in-depth theory and accompanied by a practical model, illustrating the principle of external operation and vehicle systems. Based on the knowledge learned, the group decided to choose the topic: " Research Air Conditioning System And Design Teaching Model" with the main purpose of further research on automatic air conditioning systems as well as create a complete model.

The implementation team hopes that when the group's project is completed, it will make a small contribution to the school's teaching work.

Due to limited knowledge and experience, shortcomings in the process of implementing the project cannot be avoided. The group looks forward to receiving help and suggestions from the teachers to make the group's topic more complete.

<b>1.2. Purpose, scope of research: 1.2.1. Research purpose </b>

The group received a model that describes the operation of the air conditioning system at the electrical workshop in building F1. The model was quite old, not working, missing many parts and damaged quite a bit. Therefore, based on the knowledge learned along with the research process, the group implemented the following issues:

- Research on the operating principles of the automatic air conditioning system.

- Design the 3D frame of the air conditioning system model using the Inventor software.

- Assemble a complete air conditioning model with all the necessary sensors.

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- Use Arduino to collect sensor signals to display pressure and temperature values on the LCD screen.

- The group compiled a clear and detailed presentation on the theoretical basis, operating principle of the air conditioning system, as well as details of the model.

<b>1.2.2. Research scope </b>

Because this is an old model, some materials in the model were lost during the construction process, so the implementation team tried their best to replace and repair them. Therefore, some parameters on the model may be slightly different from those on the actual vehicle.

<b>1.3. Research method </b>

- Review any gaps in knowledge that may have arisen during the research process.

- Consult with your supervisor for guidance.

- Research relevant materials to complete the theoretical framework.

- Conduct multiple experiments on the model to obtain the most accurate results.

<b>1.4. The scope of application </b>

- The practical model can be incorporated into teaching and learning programs. Students can practice directly on the model under the guidance of a lecturer to gain a deeper understanding of the operating principle of the air conditioning system.

- The accompanying documentation provides a detailed description of the operation of the system, giving students a more comprehensive overview of the system they are studying.

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<b>Chapter 2: THE AUTOMATIC AIR CONDITIONING CONTROL SYSTEM 2.1. Introduction about Air Conditioning </b>

➢ <b>The Ideal Temperature Range for the Human Body </b>

The main factor that causes the feeling of hot or cold in humans is temperature. The human body typically has a temperature of 37<small>o</small>C. During exercise, the human body constantly releases heat. The amount of heat released by the body depends on the intensity of exercise.In order to maintain core body temperature, the body constantly exchanges heat with the environment. This heat exchange will vary in accordance with the intensity of exercise.

According to research by scientists, humans grow and develop best in a temperature range of 22^oC to 27^oC. In terms of humidity, the humidity level that is good for human health is at 55% to 65%. Humans tend to still feel comfortable if the humidity is high above 70% but the temperature is low below 22<small>o</small>C or the temperature is high around 28<small>o</small>C to 32<small>o</small>C but the humidity is low at only about 30%.

➢ <b> Heat and Heat Transfer </b>

In short, heat is a form of energy stored in matter due to the disordered thermal motion of the particles that make up the matter. In matter, the molecules that make up the object are constantly moving in a disordered manner, so they have kinetic energy. This kinetic energy can be divided into the kinetic energy of the motion of the center of mass of the molecule, plus the kinetic energy in the vibration of the atoms that make up the molecule around the common center of mass, and the kinetic energy of rotation of the molecule around the center of mass. The sum of these kinetic energies of the molecules is the heat energy of the object.

Heat tends to transfer from where the temperature is high to where the temperature is low, for example, we feel cool because heat from the body has been transferred to the environment with a lower temperature, lowering the temperature in that area of the body.

There are three main modes of heat transfer: conduction, convection, and radiation:

Conduction (or heat conduction) is the transfer of kinetic energy between neighboring atoms or molecules without the exchange of material. This form of heat transfer always occurs from a region of higher energy (with a higher temperature) to a region of lower energy (with a lower temperature). Heat transfer in metals through the movement of electrons is also conduction.

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Convection heat transfer is the process of heat transfer by the movement of a fluid or gas between regions of different temperatures or the transfer of heat from a solid system to a fluid (or gas) system and vice versa. There are two types of convection: natural convection (the movement of the material is due to internal energy in the fluid, gas) and forced convection (the movement is due to external forces, such as fans, pumps, etc.).

Radiative heat transfer is the transfer of heat through electromagnetic waves. Radiative heat transfer can pass through all types of materials, as well as through a vacuum. All objects with a temperature greater than absolute zero (0 Kelvin) emit heat radiation. In heat radiation, the heat flow not only flows from hot to cold, but also in the opposite direction. However, because the heat flow from hot to cold is always greater than the flow from cold to hot, the total heat flow is always in the direction from hot to cold. In other words, the temperature difference always decreases. In heat radiation, the heat flow is calculated using the Stefan-Boltzmann law.

<b>2.2. Overview of the air conditioning system </b>

An air conditioner is a device that circulates air, controls temperature and humidity in an enclosed space. Unlike ventilation, in an air conditioning system, the air has been treated for temperature and humidity before being blown into the room. Therefore, air conditioning will be more effective than ventilation.

An air conditioner in a car is a device that not only controls the temperature and circulates the air inside the car, but it also acts as a dehumidifier with the function of controlling the temperature change from high to low. It also helps to remove factors that obstruct vision such as fog, frost on the inside of the car windows.

The functions of the air conditioner in a car are:

• Control the temperature and change the humidity in the car. • Control the air flow in the car.

• Filter and clean the air.

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<b>2.3. Overview of the automotive air conditioning system 2.3.1. Classification of air conditioning systems by zone [6] </b>

➢ Dashboard installed HVAC system

Figure.2.1. Dashboard installed HVAC system

Installed under the dashboard with one single zone which is the interior space. The dashboard type has the benefit of forcing cold air directly to the occupants enabling the cooling and heating effect to be felt to a much greater degree than the system’s capacity to cool or heat the entire space. Example – the output at the air vent on an HVAC system might be 2°C which can be blown directly on to the occupant’s face for immediate cooling. The interior space will generally cool to approximately 22°C (depending on load).

➢ Boot installed single zone HVAC system

Figure.2.2. Boot installed single zone HVAC system

Installed in the boot which has a large space available for the heating and evaporators. The outlets are positioned at the back of the rear seat. Negative aspects of this design include loss of boot space and cool air streams flowing from the rear of the vehicle.

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➢ Dual zone dashboard installed HVAC system

Figure.2.3. Dual zone dashboard installed HVAC system

Generally installed at the front of the vehicle under the dashboard and extended to the rear. Dual systems can include up to three zones, driver, front passenger and the rear passengers.All zones have a set of HVAC controls to select the desired level of comfort. This system is common on high specification vehicles and MPVs (Multi Passenger Vehicles) – vehicles with a high capacity.

<b>2.3.2. Classification of air conditioning systems by control method </b>

➢ Manual type:

Figure.2.4. Manual air conditioner

This type allows manual control of the temperature with switches and output temperature with a lever. There are also levers or switches to control fan speed, control the amount of wind, and wind direction.

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➢ Automatic type

Figure.2.5. Automatic air conditioner

An automatic air conditioner controls the desired temperature by equipping an air conditioning controller and an engine ECU. The automatic air conditioner automatically controls the output air temperature and fan motor speed based on the inside temperature, outside temperature, and solar radiation reported to the control box through corresponding sensors, in order to control the inside temperature according to the desired temperature.

<b>2.3.3. Temperature control </b>

➢ Air heating system

To heat the air, a heater core is used as a heat exchanger. The heater core takes the engine’s coolant that has been heated by the engine and uses this temperature to heat the air thanks to a fan blowing into the car. Therefore, when the engine starts, the coolant temperature is still low so the heater core does not work as a heater.

Figure.2.6. Air heating system

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➢ Air cooling system:

The evaporator is used as a heat exchanger to cool the air before it is flowing into the car. When the air conditioning switch is turned on, the compressor starts working, pushing the gas (air conditioning gas) to the evaporator. The evaporator is cooled by the refrigerant and when the air is blown through the evaporator by the blower motor, it is cooled to be flowed into the car. Thus, the heating of the air depends on the temperature of the engine coolant while the cooling of the air depends on the refrigerant. These two functions are completely independent of each other.

Figure.2.7. Air cooling system ➢ Air dehumidification system:

The amount of water vapor in the air increases when the air temperature is high and decreases when the air temperature is low. When passing through the evaporator, the air is cooled. The water vapor in the air condenses and sticks to the cooling fins of the evaporator. As a result, the humidity inside the car is reduced. The water sticking to the cooling fins condenses into mist and is stored in the water drain tray. Finally, this water is taken out of the car through a conduit.

➢ Air temperature control

Air conditioning in cars controls temperature by using both the condenser and the evaporator, and by adjusting the position of the air mixing damper as well as the water valve. The air mixing damper and the water valve work together to select the appropriate temperature from the temperature selection knobs on the control panel.

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<b>2.3.4. Air distribution through the interior of the vehicle </b>

Air distribution through the interior of the vehicle A ventilator is a device used to direct air through the inside of a vehicle.There are generally two types of ventilator used on a vehicle:

- Natural flow ventilator.

<b>- Forced flow ventilator (blower) </b>

➢ Natural flow ventilator [6]

The process of taking outside air into the car due to the pressure difference created by the movement of the car is called natural flow ventilator. The distribution of air pressure on the surface of the car when it moves is indicated in the figure, some places have positive pressure, and some places have negative pressure. Thus, the intake vents are located in places with positive pressure (+) and the exhaust vents are located in places with negative pressure (-).

Figure.2.8. Positive and negative pressure across the surface of the vehicle ➢ Forced flow ventilation [6]

In forced ventilation systems, an electric fan is used to draw air into the car. The air intake and exhaust vents are located in the same position as in the natural ventilation system. Typically, this ventilation system is used in conjunction with other air systems (air conditioning system and heater).

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Figure.2.9. (a) Fresh air inlet; (b) Fresh air inlet Ford Fiesta ➢ Air filter and air purifier:

• Air filter - Uses

Figure.2.10. Air filter

An air filter is a device used to remove cigarette smoke, dust, impurities, etc., to clean the air inside the car.

- Structure:

An air filter consists of a fan, a fan motor, a smoke sensor, an amplifier, a resistor, and an activated carbon filter.

- The principle of operation of an air filter:

An air filter uses a fan motor to take air from inside the car and clean the air while deodorizing with the activated carbon in the filter.

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In addition, some cars are equipped with a smoke sensor to detect cigarette smoke and automatically start the cooling fan motor at the ‘HI’ position.

<b>2.4. The structure and operation principle of a car air conditioning system 2.4.1. The general structure of a car air conditioning system </b>

The car air conditioning system includes components: Compressor, condenser, reciever/dryer, expansion valve, evaporator, and some other devices to ensure the system operates most effectively. The figure below introduces the components in the car air conditioning system.

Figure.2.11. Air conditioning system

<b>2.4.2. The car air conditioning system operator </b>

The car air conditioning system operates according to the following basic steps [1]:

• The compressor is driven by the engine via a belt, pressurizes the gaseous refrigerant at high pressure and transfers it to the condenser (vapor phase, high temperature, high pressure).

• At the condenser, the refrigerant is cooled by the fan, due to being dissipated at a high pressure causing the refrigerant in the vapor phase to condense into a liquid phase.

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• The refrigerant continues to circulate to the receiver-dryer, where the cold refrigerant is purified by absorbing all moisture and impurities.

• The expansion valve or flow control valve regulates the flow of the liquid refrigerant into the evaporator, reducing the pressure of the refrigerant. Due to the pressure reduction, the refrigerant changes from a liquid phase to a vapor phase, with a low temperature flow into the evaporator.

• During the evaporation process, the refrigerant absorbs heat in the passenger compartment, helping cooling the air.

• The air taken from the outside passes through the evaporator. Here, the evaporator takes away a lot of energy from the air through the heat dissipation fins, so the temperature of the air decreases very quickly and the moisture in the air also condenses and is expelled. At the evaporator, when the refrigerant in the liquid phase with high temperature and pressure becomes a refrigerant in the vapor phase with low temperature and pressure. When this process occurs, the refrigerant needs a lot of energy, so it will take energy from the air around the evaporator (energy is not lost but transferred from one form to another). The air loses energy so the temperature drops, creating cold air. The cold refrigerant in the vapor phase, under high temperature and low pressure, is returned to the compressor.

<b>2.5. Structure and operating principles of some main parts in the automatic air conditioning control system </b>

<b>2.5.1. Compressor </b>

➢ Main function [6]

The compressor's function is to move and pressurize superheated refrigerant gas within a closed loop system, and it's essential to keep it clear of any liquids or dirt to avoid harm. Compressors are available in a variety of forms, sizes, weights, rotational velocities, directions, and displacements, and can be driven either mechanically or electrically. Some compressors have a variable displacement, while others have a fixed one. The compressor uses 80% of the energy required to operate an air conditioning system, which means the compressor is the most important part in the refrigeration system. The capacity, quality, longevity and reliability of the refrigeration system are mainly determined by the compressor. When converted to a gas state at low temperature and pressure, the refrigerant

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is compressed and converted into a gas state at high temperature and high pressure. It is then transferred to the heater.

➢ Types of compressors

Many types of compressors are used in automobile refrigeration systems, each type of compressor has different structural characteristics and working principles. But all types of compressors perform the same function: Receive low-pressure steam from the evaporator and convert it into high-pressure steam pumped into the condenser.

In the past, most compressors used two pistons and a crankshaft, the piston moving reciprocating in the cylinder, this type is no longer used. Currently the most widely used types are axial piston compressors and sliding vane rotary compressors.

• Through-Vane compressors - Structure

A vane compressor consists of a rotor attached to two pairs of vanes and surrounded by a compressor cylinder. Each vane of this compressor is placed opposite each other, there are 2 pairs of vanes such that each vane is placed perpendicular to the other vane in the slot of the rotor. When the rotor rotates, the vanes will be lifted radially because their tips slide on the inside of the cylinder.

Figure.2.12. Structure of Through-Vane compressors

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- Working Principle

Figure.2.13. Working principle of Through-Vane compressors

When the rotor rotates, the two vanes rotate and move forward in the groove of the rotor, while the two ends of the vanes contact the inside of the cylinder and create pressure to compress the refrigerant.

• Variable Type Compressor - Structure

As the shaft rotates, the guide pin rotates the plate diagonally through the plate whose lugs are directly connected to the shaft. This rotation of the cross plate is converted into rotation of the piston in the cylinder to perform suction, compression and discharge in the refrigerant.

Figure.2.14. Structure of Variable Type Compressor

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- Working Priciple

Figure.2.15. Working priciple of Variable Type Compressor

The valve controls the pressure in the cross-plate chamber depending on the degree of cold. It changes the tilt angle of the diagonal plate thanks to the guide pin and shaft that act as a hinge and piston stroke to control the compressor to operate appropriately.

When the cold temperature is low, the pressure in the pressure chamber drops, the valve opens because the pressure of the bellows is greater than the pressure in the low pressure chamber, from which the pressure of the high pressure chamber acts on the cross plate chamber. As a result, the pressure applied to the right is lower than the pressure applied to the left. Therefore, the piston stroke becomes smaller due to being shifted to the right.

This compressor capacity changes because of the change in suction and discharge volume according to the heat load, so the capacity is also optimally adjusted according to the heat load. This compressor capacity changes because of the change in suction and discharge volume according to the heat load, so the capacity is also optimally adjusted according to the heat load.

The compressor changes flow according to the heat load which can change the tilt angle of the plate. Changing the piston stroke helps the compressor capacity to always be adjusted and reach the highest level.

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• Scroll Compressor: - Structure:

Figure.2.16. structure of scroll compressor The compressor consists of a fixed scroll and a variable scroll.

- Working Principle:

Figure.2.17. Working principle of scroll compressor

Following the periodic motion of the variable scroll, the three spaces between the variable scroll and the fixed scroll will move to make their volume gradually smaller. That is, the refrigerant sucked in through the intake port is compressed due to the cyclic movement of the scroll and each time the scroll rotates 3 times, the liquid is discharged from the discharge port. In practice the refrigerant is drained immediately after each cycle.

• Swash Plate Type (Fixed Displacement) - Structure:

The piston pairs are arranged in a staggered pattern with a 720 degree crank angle separation for a 10-cylinder compressor or a 120 degree crank angle separation for a 6-

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cylinder compressor. When one side of the piston is in the compression stroke, the piston on the other side is in the suction stroke.

Figure.2.18. Structure of Swash Plate Type (Fixed Displacement) - Working principle:

Figure.2.19.Operation of Swash Plate Type

As the piston transitions towards the left, it triggers the opening of the suction valve. This action generates a variance in pressure between the suction shaft, which is enclosed within the apparatus, and the cylinder's interior, facilitating the entry of the refrigerant into the cylinder through the suction valve. In contrast, the rightward motion of the piston results in the closure of the suction valve and the subsequent compression of the refrigerant. As this compression persists, the refrigerant's pressure within the cylinder escalates, prompting the discharge valve to open. Consequently, the refrigerant is directed towards a pipe designed to handle high pressure. The suction and discharge valves are instrumental in averting the backward flow of the refrigerant.

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➢ Compressor oil • Function:

Compressor oil is a specialized oil for compressors, necessary to lubricate moving parts in the compressor. Compressor oil lubricates the compressor by mixing with the medium and circulating in the circuit of the air conditioning system. Therefore, it is necessary to use suitable oil. The compressor oil used in the R-134a system is not a substitute for the compressor oil used in the R-12 system. Using the wrong lubricant can cause the compressor to seize and cause damage to the compressor.

• Amount of lubrication oil in the compressor:

If there is not enough lubricating oil in the circuit of the air conditioning system, the compressor cannot be well lubricated. On the other hand, if the amount of lubricating oil in the compressor is too much, a large amount of oil will cover the inner surface of the evaporator and reduce the efficiency of the heat exchange process and thus reduce the cooling capacity of the system. . For this reason, it is necessary to maintain the correct amount of oil in the refrigeration system.

• Add oil after replacing parts:

When the refrigerant circuit is opened to the air, the refrigerant will evaporate and be discharged from the system. However, because compressor oil does not evaporate at room temperature, most of the oil remains in the system. Therefore, when replacing a part such as a dehumidifier tank, condenser or condenser, it is necessary to add an amount of oil equivalent to the amount of oil remaining in the old part to the new part.

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➢ Structure

Figure.2.20. Structure of magnetic clutch

The magnetic clutch consists of a stator (electromagnet), pulley, centering part and other parts. The centering unit is installed together with the compressor shaft and the stator is installed on the front body of the compressor.

Electromagnetic clutches work on the electromagnetic principle, there are two basic types: • Static magnetic pole type (magnetic poles are arranged on the compressor body). • Rotating magnetic pole type (magnetic poles are installed on the rotor and rotate

with the rotor, providing power through carbon brushes placed on the compressor body).

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