What Car? Q&A - Smelly air-con

Q: The air-conditioning system in my old Ford Mondeo has developed a strange smell, which appears to be getting worse. I don’t know what is causing it but it’s getting so bad that I don’t enjoy driving the car. What could be causing the stink?
David Robertson

A: The most obvious cause of the stench is bacteria within the system itself. Because an air-con system deals hot and humid air, it is easy for bacteria to thrive on the condenser part of the system.

Getting rid of the smell may not be straight-forward. You could try running the system on maximum heat for at least 10 minutes to dry the condenser out. This may remove the problem temporarily, but it is likely to return. There are kits available, from manufacturers such as Comma, which act as disinfectants and are sprayed into the air con system to kill the bacteria.

Your local garage my also be able to help although you should be wary if they say you need to replace parts of the system. This can be an expensive remedy, and is not guaranteed to work. It might be possible for them to service the system without incurring too much cost.

You can help your air-con system stay in shape by running it constantly, even in the winter. Many car manufacturers recommend that you keep the system on all the time. By continually circulating the coolant within the system all the parts are kept lubricated and in working order.

You can give your air-conditioning a workout by running it at full cold for 10 minutes, followed by full heat for 10 minutes. This not only helps the system maintain maximum efficiency, but also helps kill any bacteria hiding inside.