Air conditioning trouble shooter: find the problem with your car’s AC

driver turning air conditioning dial in car cabin

Summer’s coming, the sky will be blue (hopefully), the sun should be shining (if we’re lucky) and the inside of your car will probably be heating up. Time to switch on the air-conditioning. But what if rather than an ice-cool breeze blowing through the vents, the air is as warm as it is outside? Read our air-con trouble shooter to find out what may be wrong.

How air-conditioning works

To know what might be wrong with your air-con, you should know the basics of how it works. The heart of any air-conditioning system is the compressor. This takes the refrigerant as a low pressure gas, compresses it to be high pressure and forces it out to the condenser. This condenses the gas back into a liquid, still under pressure. The refrigerant liquid is dried before moving through a valve to the evaporator. Here it absorbs warm air from the cabin, turns back into a gas and returns to the compressor for the whole process to start again.

Air is flowing but doesn’t feel cold enough

To work efficiently, an air-conditioning system needs plenty of refrigerant. This leaks out over time. It’s estimated that on average a car loses between 10 and 15 per cent of its refrigerant ever year. This escapes through seals and microscopic holes and can get to the point where there’s insufficient refrigerant to cool the hot air. Remember, the refrigerant is a gas as well as a liquid, hence the term ‘re-gassing’ when you have it recharged.

Cool air is only produced every now and again

This intermittent air-con action could be caused by blockages. This can be from air and moisture in the system allowing ice to form which then blocks the pipes. Alternatively, it could be an electrical problem. Think of the compressor as a mini engine. The refrigerant carries the oil that’s its lubricant. To prevent damage, systems have sensors that tell the compressor not to switch on when the level of refrigerant is too low. Sometimes these sensors can be faulty.

Start the engine and turn the air-con onto max. Then open the bonnet. You should hear the revs rising and falling slightly and a clicking sound

Air-conditioning isn’t turning on

This could be a problem with the air-conditioning switch. But more likely it’s going to be a lack of refrigerant. Alternatively, there are a variety of components around the compressor that could be causing the problem. Or the compressor itself could have failed. You’ll be able to hear if the air-conditioning is switched on by parking on flat ground with the handbrake on. Start the engine and turn the air-con onto max. Then open the bonnet. You should hear the revs rising and falling slightly and a clicking sound.

Top tip

If you suspect a lack of refrigerant is the problem, it’s a good idea to have the system pressure tested for leaks. It’s a waste of money having it recharged if all that gas leaks away before you have time to use it.

Air-con troubleshooter
Garages have specialist equipment that can quickly track down air-con trouble

Your air-con smells bad

As car makers come under increasing pressure to produce more eco friendly cars, air-conditioning units are getting smaller to save weight and space. These smaller units are more efficient but provide a happy haven for bacteria to multiply in the evaporator. And bacteria smells. There’s not much you can do about this, other than to have the system professionally cleaned.

Find out where you can get your air-conditioning serviced here.



Mandy Weston

Mandy is an ex-mechanic, with 22 years’ experience in the motor industry. As an in-house motoring expert, Mandy is the go-to woman for any relevant questions that our customers have; both garages and drivers. From specific problems with your car to general maintenance, Mandy is a reliable source of information and advice. Her passion for motoring is a huge factor to her success and the huge wealth of knowledge that she has. She now uses her remarkable grasp of the industry to write regular content for our readers to help drivers understand their car better, avoid being ripped off by garages and save money on their motoring requirements.