The auto relies on temp settings from external and internal sensors, if you have it set to 20C and its 0C outside, fans on auto should not kick in straight away. It should always take a little while for fans on auto to kick in as you also have delays built in to these circuits a bit like with petrol level sensors so sloshing doesn't affect the gauge when cornering. I think 40 has the same internal sensor as 300 with a little fan bolted to panel under steering wheel to the right with a little vent in it. Might be worth undoing it and cleaning it up on any car as the thermocouple always get fluffed up and doesn't operate as it should.
richard1983 wrote:The car does have an A/C leak at the moment (hissing behind the dash), which I must sort out.
That does not have to be a leak in that area per se...
I have noticed (on a ‘94 3.3 and a ‘93 4.0) that the hiss is a ‘feature’, and happens when the refrigerant level is low, but still sufficient to activate the pressure switch...
In both cases the noise disappeared after an A/C regas.
Hope the same goes for a V12 as well?
When I took my 40 to a 'reputable' garage in Cambridge for an oil change many years ago, they tried to scare me by saying the hissing noise is from failing brakes and I have to sort it out asap... Silly muggles
1996, 3.2 SWB X300 - Finally a rust free daily driver
1997, 4.0 LWB X300 - Unlucky car.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, October 2015. Gone!
1994, 3.2S XJ40 - Long gone.