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An air conditioner collects hot air from a given space, processes it within itself with the help of a refrigerant, and a bunch of coils and then releases cool air into the same space from where the hot air had originally been collected. This is essentially how all air conditioners work.

When you switch an AC on and set your desired temperature (say, 20 degrees Celsius), the room temperature sensor installed in it senses that there is a difference in the temperature of the room’s air and the temperature that you’ve chosen.

This warm air is drawn in through a grille on the indoor unit, which then flows over some pipes which are also known as coils through which the refrigerant is flowing. The refrigerant liquid absorbs the heat and becomes a hot gas itself. This is how heat is removed from the air that falls on the evaporator coils. Note that the evaporator coil not only absorbs heat but also wrings out moisture from the incoming air, which helps in dehumidifying the room.

This hot refrigerant gas is then passed on to the compressor (inside the outdoor unit). Being true to its name, the compressor compresses the gas so that it becomes hot since compressing a gas increases its temperature. This hot, high-pressure gas then travels to the third component – the condenser which condenses the hot gas so that it becomes a liquid. The refrigerant reaches the condenser as hot gas but quickly becomes a cooler liquid because the heat of the ‘hot gas’ is dissipated to the surroundings through metal fins. So, as the refrigerant leaves the condenser, it loses its heat and becomes a cooler liquid. This flows through an expansion valve – a tiny hole in the system’s copper tubing – which controls the flow of cool liquid refrigerant into the evaporator, so the refrigerant arrives at the point where its journey started.

The entire process is repeated over and over again until the desired temperature is attained. In a nutshell, an AC unit keeps drawing in warm air and expelling it back into the room until there’s no more warm air left to cool.

Some of the main components inside an AC Indoor Unit apart from the PCB are:-

1) Blower Unit:-

It is a blower fan that rotates in such a way that from one end it takes the hot air inside and from the other end it sends out the cooled air. In this unit other than a blower there is a motor as well which is required to run this blower fan. It is a hollow cylindrical pipe sort of thing whose function is to send cool air outside.

2) Cooling coils:-

Above the Blower Unit, there is the main component that is responsible for cooling the air before it is sent out. In this unit what happens is that there are narrow pipes present from which the cooled gas coming from the Compressor continuously passes as the hot air comes near these pipes its heat and humidity are absorbed by this coil and the air is cooled which is sent outside by the blower fan. Above the coils, radiators are also present for easier transmission of heat.

When we come to the circuitry of the Indoor unit of the Air Conditioners the main components that are observed on that are:-

1) Wiring:

There are three wires coming to the inside of the Indoor unit these are for Live, Neutral, and Earth. The power to both the Indoor as well as Outdoor Units is provided through these wires as there is no direct power supply to the outdoor unit.

2) Fan Capacitor:

Now as we are inside the Indoor unit there is a fan that blows in and out hot and cool air respectively from the Indoor Unit and to drive that fan's motor this Fan Capacitor is required. Round cylinder-shaped dual run capacitors are commonly used here, to help in the starting of the compressor and the condenser fan motor whose capacitance value is somewhere around 2 uF.

3) Micro controllers:

These are the components that act as the brain of the Air Conditioner these are the decision-making unit or we can also say the controlling unit which controls the running of motors and the power transfer etc. Apart from that, these are the components that are responsible for switching the compressor ON and OFF according to the temperature readings.

4) Temperature Sensors:

There are two sensors present inside the Indoor unit of AC these two sensors are for sensing the temperature of the room and for sensing the temperature of the coil. According to the temperature sensed by these two sensors and the temperature which is set by the user the microcontroller makes the decision that whether the Compressor needs to be turned ON or OFF

5) Power Supply Unit:

From the Wiring that we mentioned earlier enters a voltage of 220V AC but the Microcontroller operates on DC Voltage that too having a lower magnitude that's why we need to provide this unit which takes the Input AC Voltage of high magnitude and converts into a DC Voltage of lower magnitude and supplies it to the Microcontroller.

6) Relay:

Apart from all these components, there is a Power Relay that connects the Indoor Unit to the Outdoor Unit and acts as a switch in between these two which decides whether the Compressor on the Outdoor unit will be turned ON or OFF.

These were the main components on the PCB of AC Indoor Unit apart from these some more important components are Explosion proof Varistor, The Display, and IR Reciever Assembly which shows the temperature set by the user and also receives the commands sent by the IR remote. There is a servo motor as well which is there to move the blade of the AC to control the direction of airflow.

Coming to the Outdoor Unit of the Air Conditioner there is no PCB as such in the Outdoor Unit as all of the Smart Work is done inside the Indoor Unit of the AC. But there are several COmponents inside this which are as follows:-

1) Compressor:

The compressor is the most important part of any air conditioner. It compresses the refrigerant and increases its pressure before sending it to the condenser. The size of the compressor varies depending on the desired air conditioning load. In most of the domestic split air conditioners hermetically sealed type of compressor is used. In such compressors, the motor used for driving the shaft is located inside the sealed unit and it is not visible externally.

2) Condenser:

The condenser used in the outdoor unit of split air conditioners is the coiled copper tubing with one or more rows depending on the size of the air conditioning unit and the compressor. Greater the tonnage of the air conditioner and the compressor more are the coil turns and rows. The high temperature and high-pressure refrigerant from the compressor come in the condenser where it has to give up the heat. The tubing is made up of copper since its rate of conduction of heat is high. The condenser is also covered with the aluminum fins so that the heat from the refrigerant can be removed at a faster rate.

3) Condenser Cooling Fan:

The heat generated within the compressor has to be thrown out else the compressor will get too hot in the long run and its motor coils will burn leading to a complete breakdown of the compressor and the whole air conditioner. Further, the refrigerant within the condenser coil has to be cooled so that after expansion its temperature becomes low enough to produce the cooling effect and this job is done by the condenser cooling fan which is an ordinary fan with three or four blades and is driven by a motor. The cooling fan is located in front of the compressor and the condenser coil. As the blades of the fan rotate it absorbs the surrounding air from the open space and blows it over the compressor and the condenser with the aluminum fins thus cooling them.

4) Start Capacitor:

It is the Capacitor that is essentially required to start the compressor or we can say initiate the compressor. It is generally a lower value capacitor in comparison to the Running capacitor which we are going to discuss soon. Its Capacitance value is somewhere around 3uF.

5) Running Capacitor:

As the compressor is started with the help of start Capacitor it is then needed to keep that compressor running for that very purpose we need a capacitor which is comparatively bigger in size as well as Value. Its value is somewhere around 35 uF

1) Motor Running Capacitor blows off:-

In this situation what happens is that the Fan Capacitor which is responsible for running the motor of the blower Fan present in the Indoor Unit is blown off due to which the blower of the AC does not starts or moves very slowly due to which it is not able to through air and hence does no cooling.

2) Start Capacitor inside the Outdoor unit blows off:-

In this case, the start capacitor which starts the compressor is either burnt up or not operates properly due to which the compressor is unable to start ultimately making it impossible for the hot gas coming from the Indoor unit to cool down resulting in no cooling from the AC. If this problem is not addressed on time it may also result in the damaging of other parts due to excessive heating.

3) Compressor turning OFF even if the room is not cool enough:-

It is not a big problem but a funny type of problem in this case sometimes what happens is that the room temperature sensor comes in contact with the coil which is very much cooler in comparison to the room. So when these readings are sent to the microcontroller, it decides that the room is cool enough and turns off the compressor.