I seem to recall that there is an engine coolant temperature sensor attached to one of the heater matrix pipes that would prevent the blower motors from ramping up to speed until the engine temperature was at least luke warm.

Mine is blowing at or near high speed out of the heater ducts at 10 °C or a little less maybe.

Am I being forgetful again, or just crazy? The schematics in RAVE clearly point out the connector and pin for the sensor.

And why do instrument lamps seem to go out when it's too cold to hold a screwdriver and the plastic is brittle? (that's a rhetorical question. I know the answer).

It might be down to the sensor not reading correctly - I think you can see what its reading with Nanocom if you have one?

The sensor is on the lower of the two aluminium pipes that go to the heater matrix next to where the O rings live. It isn't unknown for the connection to fail so unplugging it and giving a squirt of contact cleaner is often all it needs.

Thanks for the tips. Yes I have a Nanocom and I will plug it in later this week after it stops raining, and it warms back up into the 50s once more.
It's a bit awkward plugging in with my bendy problems and being located at the front of the passenger foot well. I really need to make a short extension with a 90 degree OBDII connector on it and leave it attached.

I have CRC contact cleaner and Deoxit contact cleaner/enhancer. I will use that to see if that helps.

Not only that, but I've also just discovered that I have no blades left on the interior air temperature sensor. I do have a couple of 10 mm micro fans that I picked up a while back so I'll try rigging one of those up temporarily on the front of the grill to push air through it.

Black Box sell a 90 degree cable for the Nano.

Thanks, David, for the reminder. I just checked, and it looks like I need the NCOM26 Right-hand cable.
I recall them having them, but I had forgotten, and I was unsure at the time if it would work with the dual vehicle cable I have. Being an extension and according to what it says on the website, they will work with all cables.

Be careful leaving anything plugged into the eobd port. Left a extension in mine a few days and it corroded several of the pins in the socket. There's a permanent live in there causing electrolysis. Mine does leak from the pollen filter housing getting it wet.

Thought I'd post my findings in case anyone's interested.
The heater matrix pipe sensor is as spot on as one can expect, as is the outdoor air temp sensor.
The cabin aspirator temp sensor however is reading about 18 degrees F above actual. I thought I had a spare, but either I don't or I can't find it (not unlikely) so I'm hunting for a used one without any luck so far.
I will need to check the value of the thermistor and replace it. By the printing, of course, the value won't do me any good. This may or may not explain why the thing is so insistent on blowing warm air out of the fascia vents instead of the floor. I really hate cold feet. My other P38 behaved similarly, though, so it may just be the way it's programmed.

Aspirator probably just needs years of accumulated dust cleaning off it. Squirting cleaning stuff through the little grille doesn't usually work though, it needs to be taken out to do it properly. That will be why it is blowing only warm air as it thinks the interior is already up to temperature. Mine blows air out of the vents initially then, as the interior of the car warms up, it blows onto my feet. Maybe yours is doing the same but blowing cooler air as it thinks the interior is warmer than it really is and doesn't need any more heat?

Makes sense. I have cleaned it as you say through the grill, but never removed it to do so. It's getting far too cold for me to be working on vehicles, so this will probably be on hold until April or so, along with the Discovery and the awful noise from the front end of the P38.
I would still like to source a used replacement, so I can have it refurbished and ready to install.

I have tried turning the temperature settings for both sides up to 84 degrees F, but that seems to have no effect on air distribution, only cabin temperature. I will continue manually selecting the floor outlets. That works.