Martynn Randall is technical editor at Haynes and has been with us for 30+ years. He's written more than 65 Haynes publications and has owned more than 85 cars and 60 motorbikes... so far!
Chances are that every vehicle youâve ever owned has a heater, but how many have had air conditioning? Itâs only over the past 15 years or so that air-con has become de rigueur on every new car.
However, just spend an hour sitting in a car on hot day without air-con, and youâll soon wonder how you ever managed without it.
Thatâs because on a hot day, heat emanates from everywhere â sunlight falls on the metal and glass skin of the carâs roof, body panels and windows, is conducted through the vehicleâs skin and radiated into the passenger compartment. Heat even radiates up off the road surface, warming you up from below. Uncomfortable.
And thatâs even before you have the engine running, because then the motor itself, the exhaust system and transmission all radiate a vast quantity of heat, which also finds its way into the passenger compartment.
Carrying a passenger? Theyâll be giving off warmth (not the emotional kind) too, as will you. So, when you consider all that, air-conditioning is almost a necessity.
What is air-conditioning?
Well, itâs the process by which air is cooled, cleaned and dehumidified before entering, or re-entering, the passenger compartment.
Basically, an air conditioning system removes heat from the passenger compartment by absorbing it and carrying it outside, where it is released into the atmosphere.
An air conditioning system also dehumidifies the air, which makes for rapid demisting and increased comfort.
How does air-con work?
A carâs air-conditioning system works in pretty much the same way as a domestic refrigerator. Refrigerant gas is drawn into a belt-driven compressor, and passes into a condenser mounted on the front of the radiator, where it loses heat and becomes liquid. The liquid passes through an expansion valve to an evaporator, where it changes from liquid under high pressure to gas under low pressure. This change is accompanied by a drop in temperature, which then cools the evaporator. The refrigerant returns to the compressor, and the cycle begins again.
Air blown through the evaporator passes to the heating/ventilation housing, where it is mixed with hot air blown through the heater matrix to achieve the desired temperature in the passenger compartment.
Although air-conditioning is an energy-intensive process, and increases the amount of fuel a car uses, modern systems are efficient.
Should you use air-con all year?
Many drivers believe that air-con can only be used to cool the car, and therefore use it only during the warmer months of the year.
In fact not using the air-con at least once a week can harm it, because the refrigerant acts as a lubricant for the systemâs seals and gaskets.
So you really should switch on the air-con and turn up the heat on a regular basis during the winter â the dehumidified air generated by air-con is also excellent for clearing steamed-up windows.
Is your air-con not working as well as it did?
Over time the refrigerant can leak from the system and needs to be topped up or entirely replaced. Your local garage should be able to check the carâs systemâs pressure and refill it.
However, itâs important to make sure there arenât any leaks from seals, gaskets or the compressor itself before itâs refilled, or youâll be wasting your money.
To that end, you can either take it to a professional, or you now buy kits that can seal up small leaks in the system, in much the same way as products such as Radweld can seal up your carâs cooling system.
After that, you can refill the system using an aerosol kit, which can be purchased from high street automotive shops, or the worldâs largest online shopping site, which contributor Euan Doig did with his Seat Ibiza recently.
If you want to know exactly how and air-conditioning system works, the Haynes Air-Conditioning Techbook will tell you all you need to know.
Air-conditioning FAQs
Why does my carâs air-con smell bad when I turn it on?
If you donât use your air-con system often enough, the condensation that naturally develops on your evaporator becomes a breeding ground for bacteria. If the system emits an odour when you turn it on, itâs worth investing in a new pollen filter and a can of air-con cleaner.
Most of these cans just require you to run the carâs engine and air-con, activate the can and place it in the centre console, vacate the car and shut the doors (and windows) for a few minutes. Don't leave the car unattended, though. It should make all the difference.
Will using air conditioning make my car use more fuel?
Modern air-conditioning systems are more efficient than ever, but they do cause a small increase in demand on the engine, which will make it use a bit more fuel.
However, weâd still recommend using air-con instead of putting down the windows, because the increased drag caused by open windows will increase fuel consumption far more than just switching on the air-con.
How can I make the air-con cool the car faster?
Well, itâs good if you can park in a shaded area, so the interior temperature isnât quite so high in the first place. However, this is often impractical, so when you turn on the system, make sure you activate the recirculation mode. This keeps the cooled air inside the car, which help it to cool down the interior more quickly.
And if youâre just driving at low speeds, open the windows just a crack. This can help circulate fresh air without drawing in huge quantities of hot air.
