Car Care

The science behind your air con


The temperature’s rising, and when it’s so hot outside that your ice-cream melts in seconds, you will certainly at some point be seeking cool relief in your car if you’re hitting the road this summer. Many vehicle interface systems are now designed to set your air conditioning at the press of a button, but what is actually happening in the background?

How does air conditioning actually work?

Air conditioning systems are closed circuit, operating in a similar way to how your fridge works, and they contain both high and low pressure elements.

The high pressure component, forces gaseous refrigerant (coolant) into the condenser with the compressor, which is driven by a belt connected to the engine. This process heats the compressed refrigerant which is then cooled by the condenser and turned into a liquid under pressure.

The low pressure component is what causes all the magic to happen.

The pressurised refrigerant, now a liquid, is forced through the expansion valve and evaporator. In simple terms, the low pressure coolant immediately turns into icy cold gas.

The evaporator is located inside the vehicle and the system uses the heater fan to blow air through the chilled unit, forcing the cooled air out of the vents.

How can I help my air con to perform efficiently?

On a hot day, the inside of a vehicle can reach temperatures in excess of 60 degrees Celsius which is why you never want to leave children or pets unattended in vehicles.

To help alleviate these temperatures, try to park the vehicle in shaded areas and use a windscreen shade to keep the heat off the dashboard. This will not only keep the dashboard and vents cool, it will stop the steering wheel from getting hot and uncomfortable to hold.
If your vehicle is like a sauna inside after sitting in the sun all day, you can help the air conditioning system out by opening all the windows for a few minutes to quickly expel the heat before turning on the air con. Driving with the windows down will also force the hot air out much quicker.

For best cooling results, once you have removed the hot air from the cabin, close all the windows and then use the air con in recirculation mode. This will help circulate the already-cooled air; it’s more efficient than continuously drawing in warm air from outside.

Does air-con use more fuel than having your windows down?

Driving with the windows down can create wind disturbance which lessens the vehicle’s aerodynamics, and means more effort is needed to push the vehicle along. Air conditioning use puts extra load on the engine while in operation, causing the engine to use more energy and both can contribute in a small way to greater fuel usage. We’d recommend a balanced compromise - perhaps wind the windows down at low speeds, and set the air-con for the highway to reduce drag, cabin noise and disturbance.

Why do I have a puddle of water under the car after using the air con?

A good question! The chilled gas passing through the evaporator creates condensation which freezes and melts. It is then drained outside via a hose placed beneath your vehicle. If this hose is blocked or becomes disconnected, it can result in water leaking on to the floor by your feet. So, if you don’t see a puddle forming after parking up and having used the air con, closer inspection may be needed to make sure that everything is working as it should be.

Keeping your system operating effectively

Regular cleaning or replacement of the cabin filter (if equipped) will ensure the quality of the air drawn into the cabin is free from leaves, pollen and pollutants that can gradually clog the filter.

Over time, you may notice that the system isn’t as cold or effective as it once was. Gradually, the refrigerant may lose its pressure over time and it might require a simple top-up, or there may be a fault that has caused the gas to leak. If this happens, talk to your local mechanic and get your air conditioning system checked.

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