What Car Q&A - Why does my air-con pong?

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When I switch on the air-conditioning in my Vauxhall Astra the cabin is filled with a strange pong. It’s smells more like mould than burning. Any ideas?
John Ward


The likely cause is bacteria within the air-conditioning system. It deals with hot and humid air, so bacteria can thrive in the condenser.

Getting rid of the smell might not be easy. You could try running the system on maximum heat for around 10-15 minutes, to dry the condenser out.

If this doesn’t work, try a special disinfectant that's designed to be sprayed into the air-con system. These sprays are available from manufacturers such as Comma.

To stop the smell returning, keep your air-con system in shape by using it frequently. Many car manufacturers recommend leaving it switched on at all times. By continually circulating the coolant within the system all the parts are kept lubricated and in working order, but your fuel economy will probably drop slightly.

You can give your air-conditioning a workout by running it cold for 10 minutes, then hot for 10 minutes. This helps the system maintain maximum efficiency, and kills any bacteria hiding inside.

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