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Does my Ford Focus' air conditioning need treating to get rid of an unpleasant aroma?

I have a problem with an unpleasant aroma in my car. It is a Ford Focus Zetec and has done 26,000 miles. This peculiar aroma upset my wife's stomach, so I took it to my usual garage. They said that they tracked the smell to the windscreen washer tank, which they stripped out and washed it out with bleach and the pipework. They said that the smell was getting into the car via the washers and penetrating the air-con intakes. It did not reduce the smell so I called to the Ford main service department and on the wall of their reception was a poster saying that the air conditioning should be treated annually to prevent bacterial infection in the air con. They recommended using a spray that they sold me, in the closed car and recirculation on. This I have done, yet the bad aroma still persists, though not quite so bad. Have you ever come across this problem before on Ford cars and if so, what's the remedy?

Asked on 2 October 2010 by BT, Swindon

Answered by Honest John
Bacteria accumulates in the washer reservoir, particularly in a lightly used car and, when sprayed onto the windscreen, gets in through the venting. They can be flushed out with a hosepipe. Bacteria also grow on condensation inside the ventilation trunking of an air-conditioned car. This is the reason for switching to recirculate and releasing the antibacterial bomb inside the car. The smell could also be from spilled milk in the car, or from damp underfelt.
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