Expert advice: all about air-conditioning and how to keep cool this summer

You'll quickly know if the air-con is working or not in hot weather

Air-conditioning in our cars is something we're beginning to take for granted. But for many drivers the hot summer sun is going to expose a problem they didn't know they had: their air-con isn't up to the job.

The reason for this, and something not every car owner realises, is that air-conditioning needs regular servicing. And it's not usually attended to when a car has its regular service.

Why does air-conditioning need servicing?

The gas in an air-con system is constantly leaking out through microscopic holes in the pipes and seals. It's estimated that on average a car loses between 10 and 15 per cent of this refrigerant every year. It's a continual process and happens whether you're using the air-con or not. That's why you see signs outside garages offering to re-gas air-conditioning.

How does air-con work?

Air-conditioning needs regular attention because it's full of working parts. The air-con unit lives under the bonnet with the rest of the mechanical parts and works a bit like the back of a fridge: by extracting the heat from air that passes through it. It does this using a refrigerant that's a gas. This is compressed and forced into a condenser where it's turned into a liquid. The refrigerant then moves to the evaporator where it absorbs warm air from the cabin, is transformed back into a gas and returns to the compressor for the whole process to start again.

How often do cars need an air-con service?

Typically, this should be done every three years. However, with pressure on car makers to produce ever lighter more economical cars, air-con units are getting smaller and they need maintaining every other year.

What effect will not having enough gas have?

Quite simply it's going to prevent the air-conditioning from chilling the air. It might also cause the system to stop functioning. If you think of the air-con as a mini engine, the refrigerating gas acts as a coolant. And with no refrigerant, the air-con compressor might overheat. Even if this doesn't happen, if there's not enough gas in the system, sensors may tell the compressor to shut down to save itself from serious damage.

Will an air-con service get rid of any smells?

There are different types of air-con service. A re-gas is different to and may not include an anti-bacterial cleanse. If the air coming out of the vents smells stale, a bit like it's being pumped through someone's dirty washing, there's probably a build-up of bacteria in the system. The air-con systems in modern cars are very compact, with lots of nooks and crannies for bacteria to accumulate in. Having an anti-bacterial cleanse should eliminate the bacteria and with it the smell.

Garages use specialist equipment to re-gass air-conditioning

What does an air-conditioning service entail?

First of all, the technician should do what's known as a static test. This is done with neither the engine nor air-con running. Then the system is switched on and pressure tested again. This enables the engineer to establish how much refrigerant is in the system. This lets them work out whether it's low because of natural wastage or if there's something wrong with the air-con. The technician will use a special pump to remove all the refrigerant and any moisture in the system. Finally it's refilled to the manufacturer specified level and checked once again.

Where can you get the work done?

Most independent and franchised garages will do air-conditioning re-gassing work. There are even mobile operators who will come to your home or work to do the job. It should take between an hour and an hour and a half and should cost between £50 and £80 depending on the car and who and where you have the work done. In my opinion, it's well worth it. Over time it doesn't work out that expensive and it'll keep you cool all summer long.

Nick Reid is head of automotive technology for Green Flag and is a fellow of the Institute of the Motor Industry