My experience has been that it makes a big difference whether the external temperature is below 5 degrees or not - if yes the fuel burning heater makes the car much warmer, so at the same temperature setting, with external temperature 4 degrees car is warm while external temperature 8 degrees and no sun to warm the cabin it will be colder.
In theory one should be able to choose a standard temperature for all year round, leave the setting at auto and have the car deliver that temperature. That did seem to happen on my 2004 petrol car until the final stage resistor started to fail, but the diesel seems to need the temperature turned up above what one would normally choose, especially when the external temperature is cool, but above 5 degrees. It seems more a shortfall of heating, in warm conditions the cooling effect is more consistent. Only Range Rovers since 1988
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