Potential HVAC problems - how to diagnose?

[HPsauce]

I have two potential problems, neither currently an issue, but "a stitch in time" as they say:
1. The solar sunroof intermittently is just not working. (Today it is)
2. VCDS scan of HVAC, Fault Found: 00716 - Air recirculation Flap Positioning Motor (V113) 41-00 - Blocked or No Voltage. (This fault returns immediately if cleared)

There is no discernible pattern to the sunroof issue, if it's working, even on a grey day, it's vigorous. It had a new HVAC fan motor last summer.
But where to start on prodding, poking, measuring and diagnosis? My understanding (from long ago so could be wrong) is that the switchover is done by a relay WITHIN the HVAC, so the external wiring is very simple.
I did once fit a simple override (cutoff) switch in the (earth leg of the) sunroof circuit but MJ reverted that to OEM last summer as it wasn't the best quality job.

I normally run with the auto-recirculate on and haven't noticed anything odd. The air quality sensor was showing a fault long long (years) ago but I dismantled and cleaned it and it's always been fine. Again, I understand that there are procedures that can exercise/test/reset the HVAC flaps more thoroughly, but is that advisable and how best to do it?

[ainarssems]

For the solar not working my 1st suspect would be blower motor if old- works at high current but not at low. You say it was replaced, was it new unit or 2nd hand? Or it could be poor connection/dry solder joint in relay, wiring or DC-DC converter.
The flap positioning motors are common issue, wear particles build up inside with time and they start working intermittently, then stop all together with time. If you take them off, clean and lubricate they are fine again. But access is quite hard to take them out depending which one it is. Sometimes if they are not too bad going into basic settings and giving them full range of sweep couple of times restores functionality for a while.

[HPsauce]

Thanks Ainars. The blower was a brand new D3 one (just needed a minor connector rewire) so I'm pretty sure it's not that as it works well in fairly low light; there's no correlation that I observe between varying light levels and not working - apart from the obvious one if it's really dim/dark.

I presume there's information on the Ross-Tech site about Basic Settings exercising the flaps; does it need a security code?

[Ronin]

V113 can be located in the air conditioning service manual in tech dump section, there is a whole load of info on self diagnosis there.

[HPsauce]

It's just occurred to me that the recirculation flaps etc. are under the bonnet, not inside the cabin. Is that correct, if so I can observe operation more easily.?

[MikkiJayne]

iirc, there are two motors responsible for recirc. There's one up by the bulkhead which opens and closes the actual recirc vent (which I think is V113) and then there's one on the inlet under the waffle-grille thing. It closes the inlet as it switches to recirc so you should see that moving, but you can't see the recirc flap. I'd need to go and have a look at one to be sure.

I spliced the factory wiring for the sunroof back together where you'd inserted the switch as the current was too much for your terminals and was burning them. Might be worth checking that splice is still intact.

[HPsauce]

Thanks MJ, it's a fair bet that V113 is the inaccessible one.
As long as it's not stuck on recirculate I'm not too fussed.

As for the sunroof, it's currently working, so I'll just keep an eye on it.
If I do reinstate my switch, what current is a plausible limit?
I'll probably need a better switch and higher capacity wiring/connectors anyway.
The solar charger I use as a battery maintainer is rated at a nominal 4.8W and a maximum current around 300mA and is about 1/3rd of the area of the solar sun roof.
That suggests it's not a huge current, max 2A maybe, though my wiring probably was a bit rough....

[MikkiJayne]

Given how crispy your connectors were, I would suggest 20A connectors & switch and 2.5mm² wiring at least to match the factory stuff.