I'll get the contact cleaner tomorrow. No risk of an airbag going off in my face I hope. That would ruin my day.

re: the heated screen. Am I right in thinking that there are 2 relays? 4 & 5?

Like the good book says:

CIRCUIT OPERATION
This operates only with the engine running, which is
determined by the HEVAC panel. In the off state, the
signal is at 12 volts. When the Heated Front
Windscreen is activated, the signal is switched to 0
volts. This provides the ground required for relay 5 to
be pulled in, as there is an ignition feed on the other
side of the coil provided by relay 15. This relay
energises one half of the heated screen elements.
Once relay 5 has been energised, a 12 volt signal is
provided to the coil of relay 4. The other side of the
coil is connected directly to ground, thereby
energising the relay and switching on the other half
of the elements.
There is also a feed spliced from the harness which
provides the petrol Engine Control Module with a
signal that tells the unit there will be a large electrical
load turned on/off.

Wonder why they do it that way? I could see it being worthwhile if RL4 was slugged so it took a second or two to pull in...

I would image they do it that way to avoid a massive current draw through one track in the fuse box.. possibly also so if (when) one part of it fails, it doesn't affect the whole screen, but just half.

My main thought would be due to the current draw, and just trying to manage that a bit more.

I still think that the heated screen fault is a red herring though... unless there is actually a fault in the wiring to the fuse box, the HEVAC has no way of telling if the screen i open circuit or not, as it isn't monitored.

Looking at that diagram that the wire to the fuse box goes through the infamous kick panel connectors. I just cut my drivers footwell connectors out yesterday and soldered all the wires together with heatshrink over the joins.

Most of the wires on mine were anywhere between a bit dirty to really corroded.

I would agree that it's a red herring, one side of my heated screen has been progressively failing since I've had the car to the point now where it doesn't work at all on the drivers side. I would have expected an open circuit fault to show but there's no faults on the HEVAC at all.

I'd say the pair of relays is not only to protect the tracks in the fuse box but also the relays, when working the heated screen does draw a hell of a lot of current.

No, I understand why there's a pair of relays, what I don't get is why they've wired the coil of one relay across the other half of the screen.

If the second relay took a second or two to pull in I could see it being wired that way to prevent suddenly thumping a 50A load onto the electrics but it's just a normal relay and pulls in quickly.

not got any bits yet. Shops are shut by the time I get in.

Will the HVAC clear itself if the fault is fixed or does it need clearing?

HEVAC does a self check when you turn the ignition on (one of the odd noises you hear is the blend motors being wound from one end of their travel to the other) so if a fault isn't apparent, there's no book symbol. Then there are other things that it only notices when it starts to get up to temperature so the book can come on them but if everything is working as it should, then no book.

Sounds like that temp sensor is the culprit then...or does the solar sensor only come into play once the system is up to temp?

If the solar sensor isn't working, the HEVAC just thinks the sun isn't shining.

Hasn't had a lot of use recently :(