As grateful as I am that my Air con actually works beautifully, just been topped up and blows ice cold ! For the first few minutes if running it smells like a rotten old fridge, ? can any one tell me why ? And what can I do to eliminate the pong ! I changed the cabin filter recently

Sounds like you have mould/fungus in your system. Has the air con been dormant for some time? You can buy a can of deodorizer that you set off inside the car when air con is on. Full instructions on can. Failing that, you have to take your vehicle to an expert who will inject foam that will kill off the smell causing contaminants.

I liberally sprayed half a can of Dettol all in one disinfectant spray inside the cabin with the aircon running and the cabin circulation button on. The plan was for the system to ingest the Dettol spray thus killing off any bacteria that may be lurking within.

Obviously a really cheapskate was of doing it but so far so good

Will give that a try, cheers