I have an update on my heating system.
Both expansion tanks have now been changed and coolant topped up. Check around your expansion joints for any signs of water leaks, if you do, get them changed under warranty.
I drove 320miles, outside temp of 17⁰C, I had auto on all the way down set at around 24⁰C. After waiting for engine to properly warm up, 15mins, I pressed the auto button to turn the system on. As it was morning it was initially quite chilly and the fan was blowing far stronger than it ever had on auto, I would guess it would have been fantastic speed 2-3 if it was manual.
As the vehicle warmed up the fan speed dropped.
At some point I adjusted the temp slightly cooler, at first it was fine but then it started to blow cold but the sun was shining through the safari windows and warming the car quite a bit, I turned it up slightly and it settled down to a nice normal temp in the car for the rest of the journey.
I did have a chance to try the vehicle before the longer drive and it did seem to run sensibly in auto.
I have not tried manual yet, I had a new courtesy Grenadier when mine was being fixed (approx 150miles old), and the HVAC worked as mine seems to be doing at present. I did use manual settings to see if it was possible to upset the sensors and after much trying I finally did it.
So my conclusion is, HVAC will eventually work if the dealer fixes it properly. It is a bit dim and can be confused so treat like a simpleton.