What type of diesel fuel?

[Niall]

You realise the majority of climate control systems have no regulation over the performance of the AC side of things right? The compressor is either running or its not. Theres no in between. The temperature regulation is done by mixer flaps between the air blowing over the AC condenser and the heater matrix. So regardless of if you have climate control or not, it will still use the same amount of extra fuel with the AC on....which i'm convinced is so little its not even worth thinking about