Whether you are looking to install a large multi-unit system for your office space, or you are looking for a small unit for your home, the main principles of an air conditioner are the same.

Of course, your specialist aircon installer will be happy to spend time with you, explaining in detail how to operate your AC system, and this will be set up and customised for your personal requirements.

But with so much information to take on board it can be very confusing, so here we have compiled a simple guide, broken down for you to read through in your own time.


An air conditioner is used to create and maintain an optimum temperature, and humidity level, in a building. It also contains an air filtration system that reduces allergens and pollutants.

To understand how an AC system works, it is easier to think of it as two separate sides, a cool side and a hot side, located in indoor and outdoor equipment, respectively. These two sides are linked together by a series of refrigerant filled pipes that form part of a continuous cycle.

This is known in our industry as a split system.

A window unit, or through wall unit (mainly used in America, you may have spotted them on the TV), work using the same principles as a split system, the only difference being that both the hot side and the cool side are located within the same piece of equipment.

air conditioning 2 1


In order to cool indoor air an air conditioner uses refrigeration. Utilising the simple law of physics, the refrigerant that is circulated in the air conditioner is a liquid which absorbs heat when it converts to a gas. This process is called phase conversion. A system of coils are used to force the refrigerant to convert between gas and liquid (evaporate and condense) and vice versa, in order to cool the inside temperature of your building and expel unwanted heat to the outside atmosphere.


The indoor unit contains an evaporating coil. When warm air from inside the room is blown over the low-pressure evaporator coil, via the indoor unit(s) built in fan, the refrigerant liquid inside the coil absorbs the heat and transforms to gas. Fans within the air conditioner then circulate the now cooled air to wherever it is required inside the building. This can be direct from an ‘on show’ air conditioner or via a hidden air conditioner i.e., above a ceiling which is then ducted via ceiling grilles.  Both systems will give the same results however the ducted options are normally preferred as this finish is more aesthetically pleasing.

air conditioning 4


To carry on the cooling process the system now needs to convert the gas back to a liquid again. A compressor, which sits outside the building, inside a condensing unit, puts the gas under high pressure and this process produces unwanted heat. The unwanted heat is expelled to the outside atmosphere with the help of the condenser coils and an exterior fan (also located within the condensing unit).

air conditioning 5


The refrigerant in liquid form is transported back to the evaporator where the whole process starts again. A continuous seamless cycle where liquid refrigerant, coverts to gas, absorbs heat, is compressed and returns to liquid again.

air conditioning 6

VRF/VRV Systems – simultaneous heating and cooling

If your AC unit is a combined cooling and heating system, the above processes we have explained are simply reversed. To achieve this a reversing valve is all that is needed.  This valve reverses the flow of thermal energy, changing the direction that the refrigerant travels through the system. The hot condenser coils have now become the cold evaporator coils, and vice versa. Warm air is pumped into the room and the cold air gets expelled outside.

hLQGiSgYj76IE0DL7fho AdobeStock 173671860


Three other components that you may have heard mentioned are thermostats, filters and expansion valves. In simple terms, this is what they do….


To set your room to a desired temperature you will need to use a thermostat. The air conditioner will continue to cool air until the sensor in the thermostat detects that the room has reached the correct temperature. The sensor will then detect when the temperature begins to rise, and once again power up the air conditioning unit.

QeRgcX8UqFvPLUsrTZyz Thermostat

Expansion Valves

In this article we have learnt that there is a direct relationship between pressure and temperature. An increase in pressure produces an increase in temperature. The expansion valve restricts the flow of the high-pressure liquid refrigerant from the condenser, and controls how much can pass into the evaporator coil. By restricting the flow, the refrigerant has more room to expand in the coil. The expansion causes the pressure of the refrigerant to rapidly drop, and this also causes a drop in temperature.

E9JgJhXAmmkw35j2KRC4 expansion valve


As important as maintaining a comfortable room temperature, is the quality of the air that we breathe in.

The filter cleans the air that circulates through air conditioning system. Unwanted contaminants and particulates present in the inside air, such as mould spores, bacteria, dust particles and allergens, will be trapped in your air conditioners filter.

To ensure that this part of your AC system is working properly, it is of upmost importance that they are cleaned, or replaced, regularly. This is advised to be carried out by a specialist qualified air con installer, as other issues which may occur will be spotted and dealt with correctly, such as chemical coil cleans and other items.  This will also uphold manufacturers warranties and increase the life expectancy of each system.

air conditioning 7

Hopefully, we have now answered your question ‘how does air conditioning work?’. Of course, there are many different types of complex, highly efficient systems out there, for different types of application, so to choose the correct system for your situation calls for specialist knowledge in this field.


At Evergreen we are proud of our longstanding and close working relationship with the leading experts in the industry. As experienced and accredited installers we can offer state of the art solutions for our clients across Essex, London and the Home Counties whatever their requirements.

We also have a department dedicated to all your air conditioner servicing requirements. Our qualified engineers can help you increase the efficiency, safety and life span of your air conditioning system with regular maintenance. We can help you stay environmentally friendly by ensuring your systems are running as efficiently as they possibly can, decreasing running cots and unforeseen repair costs and most importantly protect you, your employees and your work colleagues, from the health risks associated with a poorly maintained air conditioning system.

Our experienced team would be happy to assist you, so please contact us today on 08081 781 678.

Alternatively, you can email us at Or you can complete the online form to receive a response that is guaranteed within 24 hours.