List Of Abbreviations LCD : Liquid Crystal Display HVAC : heating, ventilation, and air conditioning MPVs: Multi Passenger Vehicles ECU: Electronic Control Unit HI: High LO: Low MED: med
INTRODUCTION
Reason For Choose Topic
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.
Purpose, scope of research
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
- 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
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.
Research method
- 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.
The scope of application
- 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
THE AUTOMATIC AIR CONDITIONING CONTROL SYSTEM
Introduction about Air Conditioning
➢ The Ideal Temperature Range for the Human Body
The main factor that causes the feeling of hot or cold in humans is temperature The human body typically has a temperature of 37 o 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 o C to 27 o C 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 o C or the temperature is high around 28 o C to 32 o C but the humidity is low at only about 30%
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
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.
Overview of the air conditioning system
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
Overview of the automotive air conditioning system
2.3.1 Classification of air conditioning systems by zone [6]
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
➢ 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
2.3.2 Classification of air conditioning systems by control method
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
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
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
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
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 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
2.3.4 Air distribution through the interior of the vehicle
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:
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
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)
Figure.2.9 (a) Fresh air inlet; (b) Fresh air inlet Ford Fiesta
➢ Air filter and air purifier:
An air filter is a device used to remove cigarette smoke, dust, impurities, etc., to clean the air inside the car
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
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.
The structure and operation principle of a car air conditioning system
2.4.1 The general structure of a car air conditioning system
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
2.4.2 The car air conditioning system operator
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
• 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.
Structure and operating principles of some main parts in the automatic air
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
26 is compressed and converted into a gas state at high temperature and high pressure It is then transferred to the heater
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
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
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
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
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
Figure.2.16 structure of scroll compressor The compressor consists of a fixed scroll and a variable scroll
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)
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-
30 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)
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
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
All types of air conditioning compressors on vehicles are equipped with a magnetic clutch This clutch is considered as part of the compressor pulley
Other components
The structure of the sight glass includes a cylindrical body, above which is installed a round glass that can withstand good pressure and is transparent to observe liquids The glass is pressed tightly to the top thanks to a spring placed inside On the refrigerant supply pipeline of the refrigeration system, a sight glass is installed, the purpose of which is to qualitatively signal the liquid flow and its quality As follows:
Figure.2.32 Sight glass: (a) clear; (b) foamy; (c) streaky; (d) cloudy
- Clear Sight Glass: A clear sight glass indicates that the system has the right amount of refrigerant However, it could also mean that there is a lack of refrigerant in the system, which would result in the evaporator not cooling It's important to note that a clear sight glass doesn't rule out the possibility of the system being overcharged with refrigerant This can be verified by connecting the charging trolley and checking the gauge readings
- Foamy Sight Glass: If the sight glass looks foamy or bubbly, it suggests that the system is running low on refrigerant and air might have entered the system But, occasional bubbles during clutch cycling or system start-up might be normal
- Streaky Sight Glass: If there are oil streaks visible on the sight glass, it could indicate a lack of refrigerant
- Cloudy Sight Glass: A cloudy sight glass could mean that the desiccant in the receiver-drier has broken down and is now circulating within the system
There are two types of sight glasses: One is installed at the outlet of the receiver and the other is installed between the receiver and the expansion valve
The condenser fan is used to blow cool air through the condenser to cool this unit, or blow a large volume of air through the evaporator to transfer heat to this unit
Figure.2.34 Blower motor The blower motor sucks hot air in the car cabin or from outside the car, blows it through the evaporator, transfers heat to this unit and brings cool, dry air back to the car cabin
On most passenger cars, they are equipped with two radiator fans, one fan cools the condenser, the other fan cools the radiator The speed of these two fans changes depending on the temperature of the coolant water
Blower motor: Installed near the evaporator A blower motor is a tube made of sheet steel or plastic with many blades arranged in parallel
When operating, it does not make noise like the wing type, and the air suction and pushing capacity is quite good The blower motor is controlled to operate at many different speeds thanks to the resistor installed in the control circuit
In an automobile's air conditioning system, various components must be interconnected in a sealed loop to allow the coolant to circulate Both flexible rubber tubes and rigid metal pipes are utilized for these connections
The car's cooling system has two primary types of pipelines:
- The return or suction line, which links the evaporator's exit to the compressor's suction point This line transports the refrigerant gas (in vapor form) at low pressure and
47 temperature back to the compressor, where the refrigerant's circulation cycle resumes This line can be identified as it becomes cold when the system is operational
- The outgoing line, also known as the high-pressure line, starts from the compressor's exit
It connects the compressor to the condenser, the condenser to the filter/drier, and the filter/drier to the expansion valve's entrance
When attaching the system to the compressor, a flexible hose is required, allowing relative movement between the compressor and the engine The flexible hoses used in modern air conditioning systems are made of rubber with one or two impermeable layers inside and outside, further reinforced with an impermeable nylon layer to create a leak-proof shield
Metal pipes are commonly used in the cooling system to connect fixed devices such as from the condenser to the flow control valve, from the valve to the evaporator, etc Although metal pipes are not permeable, overflow of water or battery fluid can corrode and puncture the pipe, causing leaks
The suction line that connects the evaporator to the compressor typically has the largest diameter because it carries low-pressure refrigerant vapor The suction line usually has an inner diameter of 1/2 to 5/8 inch (12.7mm to 15.9mm) The cooling fluid supply line has the smallest diameter, typically with an inner diameter of 5/16 inch (7.9mm)
Overview of the air conditioning system in cars
Figure.2.35 The Electronic Automatic Temperature Control (EATC) system
2 High pressure exhaust valve 7 Evaporator temperature sensor
The Electronic Automatic Temperature Control (EATC) system in vehicles is equipped with a microprocessor to help maintain a pre-set cool temperature stably It can independently control the temperature on the driver's side and the passenger area This automatic system can distribute cool air to the rear seats without affecting the cool air blowing to the front seats
The automatic air conditioning system is activated by setting the desired temperature with the temperature selection knob and pressing the AUTO switch The system will immediately adjust and maintain the temperature at the set level thanks to the automatic control function of the ECU
Figure.2.36 : The automatic air conditioning system
The EATC (Electronic Automatic Temperature Control) system in vehicles operates based on input from six different sources These sources include a solar energy sensor, an internal temperature sensor, an environmental sensor, an engine coolant temperature sensor, a pressure switch, and signals from the control panel
The solar energy sensor, a photovoltaic cell, is located on the dashboard and measures solar heat The internal temperature sensor, located behind the dashboard, monitors the temperature inside the vehicle cabin The environmental sensor records the external temperature of the vehicle The pressure switch cyclically controls the electromagnetic clutch of the compressor Lastly, the control panel provides signals about the desired temperature and fan speed
Upon receiving these inputs, the EATC's electronic control unit (ECU) analyzes and processes the information It then sends control signals to adjust the fan speed of the heating and evaporators, the engine's water tank fan, and modifies the mode and flow of air to maintain the desired temperature
2.7.1 The automatic air conditioning system consists of several components
Figure.2.37.The automatic air conditioning system consists of several components
10 Air mix control servo motor
11 Air inlet control servo motor
12 Air vent mode control servo motor
➢ ECU controls the Air Conditioner
Figure.2.38 ECU control A/C The ECU (Electronic Control Unit) determines the temperature and volume of incoming air based on the readings from various sensors and the initially set desired temperature Post these calculations, the ECU manipulates the air mixing flap's position, the speed of the fan, and the orientation of the air direction control flap
Figure.2.39 Room temperature sensor The vehicle's room temperature sensor is a thermistor located within the dashboard and features a suction end This end utilizes air propelled from the fan to draw in the vehicle's internal air, thereby determining the car's average temperature This sensor serves as the foundation for managing the temperature inside the vehicle
Figure.2.40 Ambient temperature sensor The vehicle's ambient temperature sensor, a type of thermistor, is positioned at the front of the condenser to gauge the car's exterior temperature This sensor identifies the external temperature to adjust the internal temperature of the car, taking into account the impact of the external temperature
Figure.2.41 Solar sensor The solar sensor, a type of photodiode, is positioned atop the dashboard to measure the intensity of sunlight This sensor identifies the sunlight's intensity and uses this information to adjust the internal temperature of the car, considering the impact of the sun's rays
Figure.2.42.Evaporator temperature sensor The temperature sensor of the evaporator employs a thermistor and is positioned within the evaporator It detects the temperature of the air as it traverses the evaporator (the evaporator's surface temperature)
This sensor is utilized to avert surface freezing of the evaporator, regulate temperature, and manage airflow during transitional periods
Figure.2.43.Water temperature sensor The coolant temperature sensor, a type of thermistor, identifies the temperature of the coolant based on the engine's coolant temperature sensor This information is relayed from the engine's ECU In certain vehicle models, the coolant temperature sensor is situated in the heater core Its function is to regulate temperature and control the process of air heating.
Servo motors
2.8.1 Air mix control servo motor
The air mixing motor includes motor, limiter, potentiometer, moving contact and it will be controlled by ECU signal
Figure.2.44 Position of air mixing motor
Figure.2.45.working principle of air mixing motor
When control plate moving to HOT point, MH pin will be electrolized and MC pin is going to ground, and air mix control servo motor activated In reverse, MC pin is electrolized and
MH pin connected to ground, air mix control servo motor change the rotate direction, moving to COOL point
When moving contact of the potentiometer syncing with the rotation of servo motor, create electricity value depend on its position and giving the information toward the ECU Right when the air mix control servo motor’s plate get to the position, the electric going to the motor will stop
The limiter that equipped for air mix control servo motor was to stop the electricity going to the motor when it end up its cycle.When moving contact move syncing with the motor, contact the end up point of its cycle, electric stopped, motor stopped
2.8.2 Air inlet control servo motor
The air inlet control servo motor consists of a motor, gears, moving discs
Figure.2.46 Position of air inlet motor
Figure.2.47 Operation of air inlet motor
When push the air selection switch, the servo motor’s electric circuit closed, the motor electrolized, controlled the plate, let the air in
The plate control the air flow to the FRESH or RECIRC, contact point of the moving disc connect to the motor seperated, the electric circuit linked with the motor will be interrupted, the motor stopped
2.8.3 Air vent mode control servo motor
The air blower servo motor includes a motor, moving contacts, motor drive circuit, etc controlled by ECU signals
Figure.2.48 Position of air vent mode servo motor
Figure.2.49 Operation of air vent mode servo motor The automotive air conditioning system has five mode: FACE, B/L (Bi-level), FOOT, F/D (Face defrost), DEF ( Defrost) When the system openratings, one of the modes activated
ECU of A/C system control the motor, open the air vents and let the air flow, follow the signal from switch modes of the dashboard
Motor drive circuit is a digital signal circuit with the input signal is the position signal of two contact points A and B, the output signal control the current’s direction moving to the motor
2.8.4 Control the outlet air temperature (TAO)
Figure2.50 Control the outlet air temperature (TAO) The objective of the Automatic A/C system is to reach an output temperature based on a preset temperature use “TAO” to represent the desired output temperature To be effective, the HVAC system must be able to deal with variables such as the number of passengers in the vehicle, relative outside temperature and the solar load in the vehicle Formaximum comfort, the system anticipates conditions that will affect the interior temperature before the temperature rises Here are the various inputs to the A/C ECU to determine TAO It is only important to be aware of the variables that determine TAO.[1]
Outlet air temperature (TAO) got low base on some conditions:
• Preset temperature get lower value
• Car’s cabin temperature get higher value
Displays temperature and pressure at the condenser and evaporator
Arduino is an open-source hardware and software platform for building interactive projects The hardware consists of a microcontroller board, sensors, and actuators The software provides a programming language and an integrated development environment (IDE) for writing and compiling code
Arduino boards are based on the Atmel AVR 8-bit or ARM Atmel 32-bit processor Current models include 1 USB port, 6 analog input pins, and 14 digital I/O pins
Arduino was introduced in 2005 by Massimo Banzi and David Cuartielles The goal of Arduino was to create an easy-to-use, low-cost platform for hobbyists, students, and professionals to create interactive devices
Arduino is a popular platform for a variety of projects, including:
Arduino is a versatile and powerful platform that can be used to create a wide range of interactive devices
Arduino Uno R3 is an open-source microcontroller board based on the Atmel AVR ATmega328P It is one of the most popular Arduino boards and is a great starting point for beginners
The Arduino Uno R3 has a number of features that make it a versatile and powerful platform for a variety of projects These features include:
• A USB interface: The USB interface allows you to connect the Arduino Uno R3 to your computer This makes it easy to program and debug your Arduino projects
• 6 analog input pins: The analog input pins allow you to connect sensors that measure physical quantities such as temperature, light, and sound
• 14 digital I/O pins: The digital I/O pins can be used to control devices such as LEDs, motors, and relays
• 6 PWM output pins: The PWM output pins can be used to generate variable-width pulses This is useful for controlling motors and other devices that require a smooth range of output voltages
Figure.2.52.Arduino Uno R3 Table.2.1 Arduino Uno R3 Specification
Digital I/O Pins 14 (of which 6 provide PWM output)
DC Current per I/O Pin 20 mA
DC current for 3.3V Pin 50 mA
Flash Memory 32 KB (ATmega328P) of which 0.5 KB used by bootloader
This is a 20x4 LCD display module that utilizes an I2C interface It's a superior quality LCD module that features 4 lines and 20 characters, and comes with integrated contrast control adjustment, backlight, and an I2C communication interface This module is particularly beneficial for those starting with Arduino as it does away with the need for intricate and bulky LCD driver circuit connections The true value of this I2C Serial LCD module is its ability to simplify circuit connections, save I/O pins on the Arduino board, and ease firmware development with the use of the widely available Arduino library
Figure.2.53 I2C Serial Interface 20x4 LCD Module Table.2.2 Specification of 20x4 LCD Module
Display Type Black on yellow green backlight
Interface I2C to 4bits LCD data and control lines
Contrast Adjustment Built-in potentiometer
Backlight Control Firmware or jumper wire
The LCD help display the values of both temperature sensors (in celcius degree) and pressure sensors (in psi) installed at the outlet hose of condenser and the outlet hose of evaporator in real-time
By observe the values of temperature sensors and pressure sensors, it helps determine the state of the refrigerant whether in vapor or liquid form, helping users, specifically students, to easily monitor the status of the refrigerant in each different modes of the air conditioning system in the most intuitive way
Table.2.3 Saturation Pressure-Temperature Data for R134A
Figure2.55 LCD display to Arduino wiring
➢ DC-DC 3A LM2596 low voltage power module
Additionally, we employed a DC-DC 3A LM2596 low-voltage power module to step down the battery voltage to meet the input voltage for Arduino
Figure.2.56 DC-DC 3A LM2596 low-voltage power Table.2.4 specification of DC-DC 3A LM2596
Dimensions 45mm (length) * 20mm (width) * 14mm
2.9.4 The temperature and pressure sensor
Our team used two sensors: Coolant Temperature Sensor for Kia Sportage 95-97 K857418840 and G1/4 pressure transducer sensor to measure the pressure and temperature values of car air conditioning gas in evaporator and condenser Based on that, we concluded the current state of the refrigerant, which helps students to understand the car air conditioning system better
The team used a Coolant Temperature Sensor for Kia Sportage 95-97 K857418840 to collect and display the temperature value of the refrigerant gas in the car's air conditioning system [3]
Figure.2.57 Coolant Temperature Sensor for Kia Sportage 95-97 K857418840
Table.2.5 Specification of Coolant Temperature Sensor
Sensor type Coolant temperature sensor
Operating temperature range -40 to 125 degrees C
We decided to use the Steinhart and Hart Equation for the temperature sensor This is an empirical expression that has been determined to be the best mathematical expression for the resistance-temperature relationship of an NTC thermistor and an NTC probe assembly [7]:
Figure.2.58 Steinhart and Hart Equation 1
“A”, “B”, and “C” are coefficients derived as follows:
We determine 3 resistance values corresponding to 3 temperature values: low, medium and high
Figure.2.59 Steinhart and Hart Equation 2-4
⇒ 𝐴 = 𝑌 1 − 𝐿 1 (𝐵 + 𝐶𝐿 1 2 ) Figure.2.60 Solving the Steinhart and Hart Equation for Coefficients
Figure.2.61 Sensor raw data vs Steinhart and Hart Equation Chart Table 2.6 Sensor raw data vs Steinhart and Hart Equation
Steinhart Equation Sensor Raw Data
Temp (Celcius) Resistanc e (Ohms) Temp (Celcius) Resistanc e (Ohms)
Table.2.7 Specification of pressure sensor
Output Signal Type Analog sensor
Wire Red: power, black: ground, green: signal
We using this formola to convert a raw pressure value to a pressure value in PSI (pounds per square inch) based on the known parameters of a pressure sensor [3]
- Vsensor: voltage value read from the sensor
- Vmin: The minimum voltage value of the sensor
- PSI: The maximum pressure the sensor can measure
- Vmax : The maximum voltage of the sensor
Figure.2.63 Pressure value of the model in compared with pressure gauge
DESIGN AND BUILD THE AIR CONDITIONING SYSTEM MODEL
Mechanical Design
Autodesk Inventor Professional is a software for building 3D models, designing, prototyping, and testing product ideas Inventor creates accurate simulation prototypes of volume, pressure, friction, load, etc., of product objects in a 3D environment Simulation and analysis tools integrated in Inventor allow users to design from basic casting to advanced levels such as detailed machine design, product visualization Inventor is also integrated with CAD and design communication tools to enhance the productivity of CAD and reduce error occurrence, saving time
Figure.3.1 Autodesk Inventor Professional Those who are using or will use AutoCAD will inherit many benefits from Inventor Professional Inventor provides a design environment and shortcuts similar to AutoCAD, supports DWG files, allowing users to switch from current 2D drawing to 3D model building Inventor is widely used in creating digital prototypes, models created from 2D AutoCAD drawings are integrated and 3D data, forming a virtual product In this way, engineers can design, simulate products without having to create physical models Users can use the 3D mechanical design tools in Inventor to study and evaluate models more conveniently and efficiently AutoDesk Inventor also offers other tools and features to
72 enhance productivity such as: Integrated Data Management, Design Automation, Automatic Drawing Updates and Views, Automatic Bill of Materials,
Figure.3.2 Inventor Professional sketch interface
3.1.2 Frame Design on Inventor Professional
To minimize errors in the frame construction process, the team uses the 3D simulation software Inventor Professional for design and calculation to achieve the highest accuracy When assembling the details of the model onto the frame, it ensures durability and aesthetics
Figure.3.3 The model framework designed in Inventor Professional
Figure.3.4 2D design of the model frame
Frame Construction and Part Search
Based on the available frame and simulation design, we calculate the preliminary necessary materials:
- Square steel pipe, 6m long, 40x40 mm, 2mm thick (2 bars)
- L-shaped iron, 77m long, 2mm thick (2 bars)
- Other supporting tools: welding machine…
The construction is carried out at the electrical workshop in building F1
3.2.1 Searching for Replacement Parts in the Car Air Conditioning System
The team was able to find and purchase a filter on Hanoi Highway Then, the team continued to search for a used condenser at Quoc Viet 's air conditioning garage on Hanoi Highway
Based on the calculations, our team proceeded to cut the steel to the exact dimensions as designed, ensuring compactness and high economic efficiency
The team used the Mig-CO2 welding machine equipped at the F1-Building workshop to weld the steel bars together
The grinding of the frame helps to remove the excess material surface after the welding process, aiming to create a flat frame surface in preparation for the painting step
Then, the team used sandpaper to rub each bar on the frame, so that when painting, the paint will adhere more firmly
3.2.5 Cutting the gas pipe and Mounting the Model Parts on the Frame
Calculate the length of the high and low pressure pipes from the compressor to the condenser and evaporator just fit enough to save costs and bring high aesthetics
The team chose green to paint the frame The team used a spray paint can instead of a brush to achieve a glossy, aesthetically paint finish.
Restoring the Electrical Circuit of the Model, Designing Electrical Panel with
3.3.1 Restoring the Electrical Circuit of the Model
Since all the electrical wires of the system are old, some are damaged, the team proceeded to cut the wires and make adjustments
3.3.2 Designing Electrical Panel with AutoCAD
Based on the previously fabricated electrical panel frame and calculating the position of the details, the team has simulated the following electrical panel:
Figure.3.5 Designing Electrical Panel with AutoCAD
Completing the Electrical Construction of the Model
Figure.3.6 Front of the heater control
Figure.3.7 Back of the heater control
Table.3.1 Symbols and Meanings of Jack Pins
B-1 AMH Control signal of air mix control servo motor (heat)
B-2 AMC Control signal of air mix control servo motor (cool)
B-3 AIF Air Control Signal inside of the Car
B-4 AIR Air Control Signal outside of the Car
B-9 BLW Blower motor Control Signal
B-11 FACE Air flow to the body control signal
B-12 B/L Air flow to both the body and floor control signal
B-13 FOOT Air flow to the floor control signal
B-15 F/D Air flow to the car floor and defogging the glass control signal B-16 DEF Air flow help defogging the glass control signal
B-20 LOCK IN Locking Magnetic Clutch signal
B-22 DIN To data link connector
B-23 DOUT To data link connector
A-1 S5 5-Volt voltage from Heater Control
A-2 TR Room Temperature sensor signal
A-3 TAM Ambient Temperature sensor signal
A-6 TE Evaporator Temperature sensor signal
A-7 TW Coolant Temperature sensor signal
A-9 TP Air mix control servo motor position signal
A-10 TPI Air inlet control servo motor position signal
C-2 ACC 12-Volt voltage when switch to ACC position
C-5 IG Power supply to Heater Control
3.4.2 Electrical circuit diagram of air conditioning system
➢ Electrical circuit diagram of the Lexus ES300 1996 air conditioning system [4]
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
Completing the automatic air conditioning system model
3.5.1 Instructions for using the model, operating the model, safety precautions during operation
➢ Instructions for using the model:
• Power up the system: Using 1-phase electric power to supply the generator.Also using battery with 12- 14V to supply the electrical system of the model
Step 1 : Turn on the generator’s switch
Step 2 : Turn on IG switch on the model
Step 3 : Push the AUTO button on the heater control
Once the AUTO button is on, the magnetic clutch on the compressor closed, helps the compressor operate by received load from the generator, and the model is ready to use
Figure 3.10 Heater control buttons Using buttons and knob on the heater control panel to control the model while operating:
• MODE button: control the air vent mode servo motor by changing between 4 mode(FACE, BI-LEVEL, FOOT and FOOT/DEF)
- FACE: Air flow to body
- BI-LEVEL: Air flow to body and flat
- FOOT: Air flow to flat
- FOOT/DEF (F/D): Air flow to flat and defrost winscreen
• A/C button: Turn on and off air conditioner
• REAR button: Rear window defrost
• OFF button: Turn off the heater control panel and also the air conditioning system
• Fan button : Increase/Decrease the blower motor speed
• RECIRCULATION/ FRESH AIR mode button : Change between recirculation mode or fresh air mode
• TEMP knob : Increase/Decrease air conditioner’s temperature
• The power supply to the generator is very large, so the power supply device must be suitable to avoid overcurrent leading to damage
• Turn off the air conditioning system before disconnecting the power source
• Avoid touching the gas pipe from the compressor to the condenser because the medium is at very high temperature and pressure, easily causing burns
Table.3.2 Main parts of the model
1 Jack (A,B,C) Bring out the signal so that the current can be easily measured
2 Relay (Heater relay,A/C relay, Fan relay)
Heater relay: Provides positive power to the blower motor
A/C relay: Disconnects the magnetic clutch from the compressor
Fan relay: Disconnects the blower motor
3 Fuse (10A, 15A, 40A) Keep the system’s electrical wiring safe
4 Heater control Control functions in air conditioning system
5 20x4 LCD I2C Display the temperature and pressure obtained from the temperature and pressure sensors
6 Evaporator The air is deprived of much energy by the evaporator through the fins, thus the temperature of the air drops very quickly while the moisture in the air also condenses and is expelled
7 Generator Simulate the car engine by pulling the compressor via the belt
8 Compressor Drawn the refrigerant from the evaporator
(vapor phase, low temperature, low pressure) from the gas tank, then compressed at high pressure and transferred to the heating coil (vapor phase, high temperature, high pressure)
9 Blower Motor Draw hot air from outside the model, blow it through the evaporator that help transfer heat and bring cool, dry air out of the model
10 Gas pipe Direct the gas flow through the components in the air conditioning system (condenser, eva- porator, expansion valve, compressor)
11 Dryer Absorb all moisture and impurities to purify the refrigerant in the cooling cycle
12 Electrical Wiring System Transmit electrical current and control signals
13 Condenser The refrigerant is cooled by the fan, and due to being dissipated at a high pressure, the refrigerant in the vapor phase condenses into a liquid phase
➢ Display pressure value of refrigerant at different temperatures on the air coditioning system:
- To provide the most visual comparison of the refrigerant pressure at different air conditioning temperatures, the team has provided three images of the refrigerant pressure values at three temperature levels: MAX COLD, 25 O C, and MAX HOT in Figure 3.24, Figure 3.25 and Figure 3.26 respectively
Figure 3.24.Display pressure value at MAX COLD temperature level
Figure 3.25 Display pressure value at 25 o C temperature level
Figure 3.26 Display pressure value at MAX HOT temperature level
- The pressure sensor placed at the outlet hose of the condenser recorded 186.6 psi at the MAX COLD temperature level, 195.6 psi at 25 o C, and 220.3 psi at the MAX HOT temperature level This shows that the pressure at the MAX HOT temperature level is the highest, and the pressure at the MAX COLD level is the lowest
- Similarly, with the pressure sensor placed at the outlet of the condenser, the pressure sensor placed at the outlet of the evaporator shows that the pressure at the MAX HOT temperature level is the highest, and the pressure at the MAX COLD level is the lowest, corresponding to 38.1 psi at the MAX COLD temperature level, 42.4 psi at 25 o C, and 52.6 psi at the MAX HOT temperature level
- Overal, it can be seen that when the temperature of the air conditioner increases, the pressure of the refrigerant also increases The pressure at the outlet of the evaporator changes according to the temperature level but not much The pressure at the outlet of the heat exchanger increases significantly and the pressure value is very large
PRACTICAL EXERCISES APPLYING THE MODEL
Practical exercise on gas charging for the air conditioning system using R314a
- Perform the gas charging process
- 12 -14 Volt battery, 220V – 1-phase power supply
- Pay attention when connecting the battery terminal
- Be careful when connecting the motor to the 1-phase 220V power source
Purpose: Helps to remove air, moisture, and old gas If the old gas is not completely removed, refilling the car's gas will mix the old and new gas, reducing the lifespan of the entire air conditioning system
Step 1: Install the vacuum pump and the gas pressure gauge into the system.Figure.4.1
Figure.4.1.Connecting compressors and meters to the model
Step 2: Turn on the vacuum pump, then open both the high-pressure and low-pressure valves (turn them out)
Figure.4.2 Simulate the vacuum process Step 3: Observe the low-pressure gauge, the vacuum level must reach 750 mmHg, maintain the vacuum level at 750 mmHg and continue to pump for about 10 minutes
Step 4: Close both the high-pressure and low-pressure valves (turn them in), turn off the pump, and maintain the status for 5-10 minutes to check for leaks
Step 5: Confirm that the system is not leaking (the needle of the gauge does not move), then remove the vacuum pump
Figure.4.3 Maintain the status for 5-10 minutes to check for leaks
Install the yellow valve into the R134a gas tank
Install the gauge set and gas tank into the system:
- Close both low and high pressure valves (tighten)
- Connect the yellow hose to the gas tank and open its valve
- Press the air vent at the yellow hose of the gauge set to release the remaining air inside the hose Let the air escape for a few seconds and then stop
Figure.4.4 Press the air vent at the yellow hose of the gauge set to release the remaining air inside the hose
Charging gas to high-pressure side
Figure.4.5 Simulate the gas charging process from the high pressure side
*The engine not yet running:
- Assemble the gas tank and the gauge set into the system.Open the high-pressure valve to the maximum
- Charge a full gas into the system and then close the high-pressure valve
- Can charge quickly by inverting the gas cylinder and charging liquid gas into the system This method allows for faster charging, however, the engine must not be started and the low-pressure valve must be completely closed
- During the gas charging process, pay attention to the gas eye on the gauge set until no longer see the gas bubble, stop charging gas
Charging gas to low-pressure side
Figure.4.6 Simulate the gas charging process from the low pressure side
- Set the fan switch to the HI position
- Set the temperature selector to MAX COOL
- Start the engine, rev up to about 1500 rpm (start the generator)
Note: The above steps help simulating the actual operating state with the highest system usage when the user uses the air conditioner
- Close the high-pressure valve, slowly open the low-pressure valve
- The system is good at the low-pressure side reaches 1.5 – 2.5 kgf/cm2 and the high- pressure side reaches 14 – 16 kgf/cm2
- Close the low-pressure valve
- Remove the gauge out of the system
Exercise to detect faults in air conditioning system using gas pressure gauge[2]98 1 Purpose
- Test the system through the pressure gauge
- Find the cause and find the way to fix the cause
- Power supply for the motor: 1-phase electricity 220V
- Pay attention when connecting the battery
- Disconnect the 1-phase power before connecting to the generator
- Check for system leaks before proceeding
- Connect the battery, 1-phase electricity, and pressure gauge to the model when charging gas
- Observe the pressure on the gauge
➢ Air conditioning system when working normally
Figure.4.7 pressure value when system working normally
The air conditioning system is properly filled with gas and functioning normally when:
- The low pressure is 1.5 – 2.5 kg/cm 2
- The high pressure is from 14 – 16 kg/cm 2
- It feels cold when touching the low-pressure pipe
- It feels warm when touching the high-pressure pipe (from the condenser – expansion valve)
- The air coming out is cool
However, these values are general Actual values may vary due to the surrounding environmental temperature and the technical characteristics of the vehicle
➢ Air conditioning system when leaking
Figure.4.8 pressure value when leaking Symptom: The pressure on both the low and high-pressure sides is higher than normal, the air in the car is only slightly cool, when the clutch is engaged/disengaged the pressure on the low side does not change
Cause: Due to the vacuum pumping process not being achieved or the vacuum pump is poor, or air leaks into the system during gas charging
Remedy: Release the gas, and vacuum again very carefully (about 15 minutes) with a good vacuum pump to ensure the low-pressure gauge returns to the level of -750 mmHg (-100 kpa = -1 bar = -1 kg/cm2)
➢ Air conditioning system operation when it is low on gas
Figure.4.9 Pressure value when the system lacks gas Phenomenon: Low pressure is low, high pressure is low The air in the car is not very cold Touching the low-pressure pipe is only slightly cold
Cause: Lack of gas, due to the system leaking
- Need to disassemble the entire system to test for leaks to find the cause of the leak (because this is a closed-loop system, it can leak at any part) Then proceed with the maintenance process
- If the system does not leak, proceed to recharge the gas
➢ Air conditioning system has poor cooling
Figure.4.10 Pressure value when the system has poor cooling
Phenomenon: The low pressure is normal, the high pressure is high The air in the car is not cool The high-pressure pipe feels very hot when touched
Cause: The cooling fan does not rotate or rotates weakly, not providing enough air to cool the condenser The gas cannot dissipate heat because the system has too much oil covering the entire surface of the heat sink, or there is too much gas so the cooling system cannot respond in time Or the condenser is too dirty, blocking the fins, and the air circulation for cooling is restricted
Remedy: Check the above conditions to come up with a remedy such as: replace the condenser fan, handle the fan's electrical system if the fan loses power or does not run at the correct speed Release gas and drain some oil from the compressor if it's too much If the condenser is too dirty, it needs to be cleaned
➢ Air conditioning system having the broken compressor, the dryer is off
Figure.4.11 Pressure value when the system having the broken compressor, the dryer is off Phenomenon: The high pressure is low, the low pressure is high The air in the car is not cool The high-pressure pipe does not feel warm When released a bit of gas, it smells bad and the oil turns dark
Cause: The compressor is broken (the parts worn out create large gaps, not compress enough pressure) Or the compressor control valve is stuck in the always open state (the high-pressure chamber is always connected with the control chamber) And the case where the condenser is blocked leads to not supplying enough gas to the compressor
Remedy: Replace the compressor for the first two cases, replace the condenser for the latter case When replacing the compressor, note that you need to replace the gas filter, clean and rinse the entire system to dislodge the sediment and oil inside, replace the new oil, vacuum and recharge enough new gas Especially with the system using a control valve, consider replacing the heat sink because the heat sink dissipates poorly, and the heat sink is the first place the compressor pushes the refrigerant and metal particles, dirty oil to And the expansion valve should also be replaced in this case to ensure the system is safe and operates effectively
➢ Air conditioning system is blocked by the expansion valve
Figure.4.12 Pressure value when the system is blocked by the expansion valve
Phenomenon: The low pressure is low (can return to vacuum pressure which is below 0 bar/cm 2 ) and the high pressure is low The air in the car is not cool Touching the pipes on both sides, they are neither hot nor cold
Cause: The capillary tube expansion valve is blocked due to dirt stuck on the flow tube of the valve The capillary tube expansion valve is blocked due to dirt stuck on the flow tube of the valve
Remedy: Replace the expansion valve Carry out the maintenance process, clean and maintain the entire system, replace the gas filter, replace the new oil, vacuum, and recharge new gas If the system inside is too dirty, the oil changes color, you need to replace the dryer in this system
Exercise of measuring the voltage of the air conditioning system
- To practice for students the method of testing and measuring the electrical system
- To determine the voltage values of the sensors and then understand the errors of the system
- Pay attention to connect the correct accu poles
- Choose the correct scale of the VOM meter
- Connect the accu to the model
- Adjust the VOM meter to the DCV 20V scale
- Connect the VOM in parallel with the circuit to be measured
- Record the values just measured and compare with the table
Table.4.1 The standard value measured between the pins
HR ⇄ GND Turn on blower motor Below 1V
FR ⇄ GND Turn on fan at MH or MC mode Below 1V
Turn off fan and normal mode 10-14V
PSW ⇄ GND Turn on switch Below 1V
TR ⇄ SG Depends on the temperature inside the car
TAM ⇄ SG Depends on the ambient temperature
TE ⇄ SG Depends on the evaporator temperature
SG ⇄ GND Always in circuit 1 Ω or smaller
TW ⇄ SG Depends on the engine coolant temperature
TS ⇄ SG Depends on the solar energy Below 1V
TP ⇄ SG Turn on switch, MC 3.5-4.5V
TPI ⇄ SG Turn on switch 0.5-4.5V
+B ⇄ GND Connect to the battery’s anode 10-14V
ACC ⇄ GND Turn on switch 10-14V
Always in circuit 1 Ω or smaller
IG ⇄ GND Turn on switch 10-14V
Exercise of testing the operation of the motors on the model
- To practice for learners the method of testing the operation of the details on the car air conditioning system
- To determine the operation of the servo motor
- Pay attention to connect the correct battery poles
- Connect the battery to the model
➢ Testing Air mix servo motor
Figure.4.13 Circuit diagram of air mix servo motor Step 1: Remove the motor from the model
Step 2: Supply power to pins 2 and 6 of the air mixing motor as shown in Figure 4.13
Figure.4.14 Supply power to the air mixing motor Step 3: Observe the movement of the motor as shown in Figure 4.13, it needs to rotate slightly to the cooling side and vice versa
If the motor is not working properly, we should replace it
➢ Testing Air inlet servo motor
Figure.4.15 Circuit diagram of air inlet servo motor Step 1: Remove the motor from the model
Step 2: Supply power to pins 1 and 2 of the air intake motor
Step 3: Observe the movement of the motor, it needs to move to the REC position and vice versa, it needs to move to the FRS position as shown in Figure 4.15
If the motor is not working properly, we should replace it
Figure.4.16 Supply power to the air mixing motor
➢ Testing Air vent mode control servo motor
Figure.4.17 Supply power to the air vent mode control servo motor
Step 1: Remove the air motor from the model
Table.4.2 The meaning of the pins on the servo motor of each wind direction modes
Step 2: Supply power to the wind direction control motor as shown in Figure 4.16
Step 3: Check the operation of the air motor.
Exercise of measuring the sensors
- To measure the voltage of the sensors
- To find the causes and solutions for the problem
- Pay attention to connect the correct battery poles
- Choose the appropriate scale of the VOM meter
- Connect the battery to the model
- Select the suitable scale of the VOM meter
Figure.4.19 Circuit diagram of Solar Sensor
The working principle of the solar sensor: The solar sensor is composed of a photodiode sensitive to infrared light, it allows electric current to pass through when light shines on it The conductivity of the photodiode depends on the amount of light shining on it
Measurement procedure: Use an infrared source to shine on the sensor Then use the VOM meter to measure the change in voltage of the sensor to see if the sensor is still working
Figure.4.21 Circuit diagram of Evaporator temperature sensor and room temperature sensor
- The working principle of the TE and TR sensors: The TE and TR temperature sensors are a type of thermistor with a negative temperature coefficient (NTC) When the temperature increases, the resistance of the sensor decreases and vice versa The change in
111 resistance value will change the voltage value sent to the heater control base on voltage divider circuit law
+ Measure the voltage of the two sensors when the model is not running, see the current temperature corresponding to the voltage level of the sensor
+ Then run the model Measure the change in voltage and temperature of the two sensors.
Exercise of checking the outside of the air conditioning system model
➢ When using the refrigerant ,follow these notes:
- Do not handle the refrigerant in a closed room or near fire
- Always wear eye protection glasses
- Be careful not to let the refrigerant stick to your eyes or skin If the refrigerant sticks to your eyes or skin, then:
+ Rinse the injured area with cold water
+ Apply clean vaseline to the skin, go to the doctor, hospital immediately to get the necessary care and treatment
+ Do not try to treat yourself
➢ When replacing the parts on the refrigerant pipe:
- Recover the gas into the gas recovery device for reuse
- Seal the parts that have been removed to prevent dust and moisture from entering
- Do not leave the new condenser or dryer… lying around without being sealed
- Release the nitrogen gas from the charging valve before removing the cap from the new compressor If you do not release the nitrogen gas first, the compressor oil will spray out with the nitrogen gas when you remove the cap
- Do not use a welding torch to bend or extend the pipes
4.6.2 Perform a outside inspection and diagnosis
If the drive belt is too loose, it will slip and cause wear Replace the belt when the belt is worn
Check for dust clogging in the air filter
➢ Hear noise near the air compressor:
Check the bolts that hold the air compressor and the bolts that hold the bracket
➢ Hear noise inside the compressor:
The noise may be due to damage to the internal parts
➢ The fins of the condenser is dirty:
If the heat sink of the condenser is dirty, the pressure of the condenser will drop sharply All dust on the condenser must be cleaned
➢ Oil stains at the joints of the cooling system or the joints:
Oil stains at the joints or joints indicate that the refrigerant is leaking from that position If such oil stains are found, they must be tightened or replaced if necessary to prevent refrigerant leakage
➢ Hear noise near the fan of the evaporator:
Rotate the fan motor of the evaporator to the positions LO, MED and HI If there is abnormal noise or abnormal rotation of the motor, the fan motor of the evaporator must be replaced Objects stuck in the fan of the evaporator can also create noise and the assembly of the motor can also make the motor rotate incorrectly so all these causes need to be checked thoroughly before replacing the fan motor of the evaporator
➢ Check the amount of refrigerant through the gas eye:
If you see a large amount of bubbles through the sight glass, it means that the amount of refrigerant is not enough so you have to add more refrigerant In this case, you also need to check the oil stains as presented above to ensure that there is no refrigerant leakage If you
113 do not see bubbles through the observation hole even when the condenser is cooled by pouring water on it, it means that the condenser has too much refrigerant so you need to remove some refrigerant only to a necessary amount When the system uses a condenser having auxiliary cooling, the refrigerant may not be enough even when no bubbles are seen.
The process of diagnosing system errors of the model
During operation, the model may generate some errors that make the system not work or work unstably Therefore, our team has built a diagnostic process to find out the cause and find ways to fix the errors for the model
CONCLUSION
Conclusion
- Following a period of diligent research and study, coupled with the meticulous guidance of our mentor, our team has successfully executed the project titled "Research Air Conditioning System And Design Teaching Model" We have also managed to introduce some innovative features that make the model more user-friendly and applicable in a teaching context
- The finalized model is ready for immediate use However, due to the use of some non-standard materials, occasional measurement errors may occur The model we received was old, leading to the malfunctioning of several structures within the condenser, evaporator Despite our best efforts, we lacked the necessary information for repairs, resulting in some deficiencies in the model During operation, certain parts experience localized heating and the noise level is relatively high, but these issues do not significantly impact the overal functioning of the system
- The team also using Arduino Uno R3 and LCD I2C to continuously display the temperature and pressure of the refrigerant during the operation of the model This helps users, specifically students, to easily monitor the status of the refrigerant in different temperature level of the air conditioning system in the most intuitive way
- The team has compiled a comprehensive explanatory manual based on specialized literature and insights gained during the model construction This ensures the provision of a thorough understanding of the air conditioning system and the operation of the model.
Constraints
- The compressor of the model lacked a lock sensor, resulting in ineffective signal reception from the sensor for the machine's correct operation
- The compressor use R12 refrigerant, which is a stop production The team use R- 134a for a replacement so the cooling efficiency cannot compared to the origianl one
- The model lacked of room temperature sensor, which the team had found the replacement, resulting in ineffective signal reception from the original sensor for the machine's correct operation
- The temperature sensor does not provide enough data that required for the system, the team have not fixed yet.
Prospective Developments
The team has several suggestions for the future progression of this project, as follows:
- Investigate and create simulations on software and fabricate the malfunctioning mechanisms that control air flow
- Affix the frame and motor to the structure via welding, enabling them to function automatically based on the operational principle
- Acquire sensors identical to those in the model to facilitate stable and accurate signal transmission
- Replace the current compressor with a sensor-equipped variant to facilitate accurate operation based on signals from other sensors
- Drawing from the team's model, future students can explore programming the system to control air flow mechanisms and temperature regulation via a smartphone, eliminating the need for manual button pressing
[1] TOYOTA Air Conditioning and Climate Control Course 752, 216 pages
[2] Lexus ES300 Service Manual and Wiring Diagram,Forum Otohui, https://oto-hui.com/ [3] Arduino, https://www.arduino.cc/
[4] Lexus ES300 1996 Electrical Wiring Diagram,Air Conditioning, Carmin Application [5] Compressor,Condenser,Evaporator, Receiver Dryer, https://aftermarket.denso.com.sg/
[6] Steven Daly (2006), “Automotive Air Conditioning and Climate Control Systems”, 382 pages
[7] NTC Thermistors Steinhart and Hart Equation, https://www.ametherm.com/thermistor/ [8] Electrics LEXUS LEXUS ES300, https://lexus.7zap.com/
[9] Water temperature sensor and pressure transducer sensor, https://www.amazon.com/
Appendices Measuring temperature and pressure in condenser
LiquidCrystal_I2C lcd(0x27, 20, 4); const float steinconstA = 0.00494838599138165000000; const float steinconstB = -0.00059485520380309200000; const float steinconstC = 0.00000664029106104212000; int samples[NUMSAMPLES1]; const int pressureInput1 = A2; const int pressureZero = 0.5 * 1024 / 5; const int pressureMax = 4.5 * 1024 / 5; const int pressuretransducermaxPSI = 300; const int baudRate = 9600; const int sensorreadDelay = 100; float pressureValue1 = 0; void setup() {
Serial.begin(baudRate); lcd.init(); lcd.backlight();
118 void loop() { uint8_t i; float average1; for (i = 0; i < NUMSAMPLES1; i++) { samples[i] = analogRead(coolantsensorPin1); delay(100);
} average1 = 0; for (i = 0; i < NUMSAMPLES1; i++) { average1 += samples[i];
} average1 /= NUMSAMPLES1; average1 = (coolantsensorDivider * average1) / (1023 - average1); float steinhart1 = log(average1); steinhart1 = pow(steinhart1, 3); steinhart1 *= steinconstC; steinhart1 += (steinconstB * (log(average1))); steinhart1 += steinconstA; steinhart1 = 1.0 / steinhart1; steinhart1 -= 273.15;
Serial.println("Ohm"); lcd.setCursor(0, 0); lcd.print(" -CONDENSER -"); lcd.setCursor(0, 1); lcd.print("Temperature: "); lcd.print(steinhart1, 0); lcd.setCursor(16, 1); lcd.print("*C"); pressureValue1 = analogRead(pressureInput1); float V = pressureValue1 * 5 / 1024; pressureValue1 = ((pressureValue1 - pressureZero) * pressuretransducermaxPSI) / (pressureMax - pressureZero);
Serial.println("psi"); lcd.setCursor(0, 2); lcd.print("Pressure: "); lcd.print(pressureValue1, 1); lcd.setCursor(17, 2); lcd.print("psi"); delay(sensorreadDelay); delay(1000);
Measuring temperature and pressure in evaporator
LiquidCrystal_I2C lcd(0x27, 20, 4); const float steinconstA = 0.00494838599138165000000; const float steinconstB = -0.00059485520380309200000; const float steinconstC = 0.00000664029106104212000; int samples[NUMSAMPLES1]; const int pressureInput1 = A2; const int pressureZero = 0.5 * 1024 / 4.95; const int pressureMax = 4.5 * 1024 / 4.95; const int pressuretransducermaxPSI = 300; const int baudRate = 9600; const int sensorreadDelay = 100; float pressureValue1 = 0; void setup() {
Serial.begin(baudRate); lcd.init(); lcd.backlight();
} void loop() { uint8_t i; float average1;
121 for (i = 0; i < NUMSAMPLES1; i++) { samples[i] = analogRead(coolantsensorPin1); delay(100);
} average1 = 0; for (i = 0; i < NUMSAMPLES1; i++) { average1 += samples[i];
} average1 /= NUMSAMPLES1; average1 = (coolantsensorDivider * average1) / (1023 - average1); float steinhart1; steinhart1 = log(average1); steinhart1 = pow(steinhart1, 3); steinhart1 *= steinconstC; steinhart1 += (steinconstB * (log(average1))); steinhart1 += steinconstA; steinhart1 = 1.0 / steinhart1; steinhart1 -= 273.15;
122 lcd.setCursor(0, 0); lcd.print(" -EVAPORATOR -"); lcd.setCursor(0, 1); lcd.print("Temperature: "); lcd.print(steinhart1, 0); lcd.setCursor(16, 1); lcd.print("*C"); pressureValue1 = analogRead(pressureInput1); float V = pressureValue1 * 5 / 1024; pressureValue1 = ((pressureValue1 - pressureZero) * pressuretransducermaxPSI) / (pressureMax - pressureZero);
Serial.println("psi"); lcd.setCursor(0, 2); lcd.print("Pressure: "); lcd.print(pressureValue1, 1); lcd.setCursor(17, 2); lcd.print("psi"); delay(sensorreadDelay); delay(1000);