How do I clean my car's air conditioning system?

I recall that you gave advice some time ago regarding 'fumigating' the air conditioning and ventilation system to get rid of noxious smells. I've tried to locate this in your FAQ's and forums with only...

How should I get bird faeces off my paintwork?

What is the best method of removing bird pooh from the paint work?

Do I really need to have a fuel system clean every six months?

Nissan have advised me that they recommend a fuel system clean every six months and will carry one out automatically when they service my car, unless I request otherwise when I book the service. Is such...