Car air conditioning 101

Knowing how air con works can help you get the best out of it

Despite summer drawing to a close, we’ve been experiencing hot, muggy days over the past few weeks. During these times, car air conditioning can be working overtime.

The air conditioning systems in many modern vehicles can be set at the press of a button, but do you know what actually happens in the background?

Air conditioning operates in a similar way to a household fridge, using pressure to transform liquid into an icy-cold gas, which the fan then blows through in order to make the cabin cool.

How can I help air conditioning perform efficiently?

On a hot day, the inside of a vehicle can reach over 60C, which is why you should never leave children or pets unattended inside. To help reduce cabin temperature, try to park in a shaded area and use a windscreen shade to keep the heat off the dashboard.

If your vehicle has been sitting in the sun all day and is like a sauna, it’s best to open all the windows for a few minutes to expel the heat before turning on the air conditioning. Driving with the windows down will also force the hot air out much quicker.

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

However, don’t use the recirculation mode for too long, as the air in the cabin could get a bit stuffy and make the driver drowsy. A blast of fresh air from an open window will help, or switch off the recirculation button and put the air con back into auto mode.

Does the air-conditioning 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 required to push the vehicle along.

Air conditioning can put extra load on the engine while in operation, causing it to use more energy and so contribute in a small way to greater fuel usage. We would recommend a balanced compromise — wind the windows down at low speeds, and set the air con for use on the highway to reduce drag, cabin noise and disturbance.

It’s important to remember that a vehicle A/C system is run by a belt attached to the vehicle engine, so only operates when the engine is running. Don’t be fooled by the few seconds of cold air still circulating once the engine is switched off; vehicles can quickly become like an oven once the cool air stops.

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

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

Keeping air conditioning 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.

Over time, you may notice that the system isn’t as cold or effective as it was. The refrigerant can gradually lose its pressure and might require a 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 the system checked.

The benefits of visiting an AA Motoring site

If you think it may be time for you to have your vehicle serviced, come and see the experts at one of our AA Auto Centres nationwide. AA Members receive additional benefits:

●Save between $10-$30 off the next service

●Save $7 off the cost of a Warrant of Fitness (WoF)

●Up to two free 10-Point Checks each year

●Boost AA Smartfuel discounts with 5 cents per litre off when you spend $58 or more at an AA Motoring site.