How A/C works

Some of our customers are interested in understanding how air-conditioning works. Here’s a brief summary of how vehicle air-conditioning works. If you want to talk to one of our experts, don’t hesitate to contact us.


The evaporator is a plastic box containing a core of fine metal fins, located behind your dashboard. It removes heat from the cabin or exterior. Heat is attracted across the fins into the cold liquid refrigerant inside.

This heat movement adds energy to the refrigerant, rapidly raising its temperature until it changes into a gas. This is similar to the way that water accepts heat until it comes to the boil then converts to steam.

In your evaporator, the air with heat and moisture removed is then pumped into the vehicle via the vents.

In winter, this dried air is perfect for use in addition to air warmed by your heater to keep windscreens dried and free from fogging.


The compressor is a mechanical pump that pressurises and drives the refrigerant around the system. The compressor pumps the gas, formed by the evaporator, to the condensor.


The condenser is another heat exchanger, located in front of your vehicle’s radiator. Heat is released across these fins from the hot, pressurised refrigerant gas to the colder outside environment. Heat transfer is assisted by a cooling fan. As the refrigerant passes through the coils of the condenser, losing energy, it condenses into a hot liquid.

The liquid passes through the receiver-drier which absorbs any harmful moisture and acid.

The dried, high pressure liquid is then forced through the expansion valve. The valve regulates the delivery of the high pressure liquid as a spray into the relatively low pressure environment of the evaporator.

This dramatic loss of pressure causes the liquid to lose a lot of heat, allowing it to receive new heat across the fins of the vehicle’s evaporator – starting the whole process again.

All of these components are interconnected by flexible hoses.

If any one of these components fails, it causes changes in the critical temperature/pressure relationship required to make heat transfer, and hence air-conditioning, work.

Controller panels:

The controller panels are mechanical or electronic controls on your dashboard that let you regulate your air-conditioning system’s performance, blending warm and cold air to suit your comfort level. Electrical circuits, sensors and protection devices may shut the system down if it’s not operating correctly.

Pollen filters:

Pollen filters trap dust, pollen and some odours. Pollen filters get blocked up over time, reducing air flow and cooling, at which stage they need replacement (once a year or approximately every 20,000 km).


  1. Toni Rogers

    Would you please tell me how much it costs for a check of my car’s air conditioning system?

    I would like to know how it is fairing and if anything needs doing to it, then I would like to know what that will cost so I can save for it to be serviced/repaired.

    The car is a 2003 Mazda Atenza.

    Thank you
    Toni Rogers

    • Hi Toni thanks for your enquiry. Mazda Atenza models have a cabin filter to change and it is common to find a build up of debris like flies and leaves between the air-conditioning condenser and the engine cooling system radiator. This ‘thermal blanket’ stops heat dissipating like it needs to from the front of the car. Cooling fans will run more than necessary when this happens but the overall effect on the air-conditioning is that the air-conditioning system operating temperatures and pressures are higher than desirable. This can lead to the armature on the front of the compressor falling off – we see this all the time in this model. The excess temperature and pressure also encourage the system to leak refrigerant into the atmosphere. Preventative maintenance on this type of system is very beneficial – we remove the condenser to clean it and the radiator and reassemble with a new drier, refrigerant and cabin filter. To find out just what’s required for your car, bring it in for an evaluation. The check on your system is typically free of charge, but we’d let you know when you come in if that was to change in any way.

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