[s-cars] No heat diagnosis please

[Paul Heneghan]

> Date: Tue, 19 Jun 2007 12:20:03 +1200
> From: Sam Clarkson <sam at edgetoedge.co.nz>
> No Heat, I pulled the codes; 08.7 temp regulator flap sporadic block
> and 11.7 central flap sporadic block.

Ah, the old sporadic block ploy!  Fix it now before it becomes a permanent
block and a fried CC head!

> I've pulled out the temp control motor assembly no movement as I
> cycle through the temp range. The arms all move freely and smoothly
> with the TCMA out and heat comes on/off when moving them manually.
> The motor in the TCMA goes fine in both directions when directly
> connected to a battery.

The motors in these are 7V motors.  Probably won't do them any real harm to
give them a bit of 12V - they'll just run a bit faster, but I wouldn't leave
them stalled for any great length of time!

The pinout is:
1 White Motor +
2 Brown Motor -
3 Grey Pot +
4 Green Pot ground
5 Yellow Pot wiper

> Any advice as to what's next to test.

Measure the voltage being applied from the CC head - it should be able to
provide +7V across the terminals and also -7V to reverse direction.  The CC
head uses dual power opamps (and an 8.5V regulator) to generate these
voltages.

> The potentiometer? How?

I think the pots are around 5K. Measure the resistance of the wiper to
ground across the range of travel.

> The supply to the TCMA? How?

One of mine had a lot of brush debris in the armature - I think it was
conducting, so the motor didn't rotate, but drew current all the time.  By
the time I got around to looking at it, the regulator (ST L4940V85) inside
the CC head had fried - not expensive to replace (GBP1.33), but a pain to do
all the dismantling and fault finding.  The other component inside the CC
head that might fail is the opamp that drives the motor - a Siemens TCA2465
Power Op Amp.

> How do I clear/reset the codes?

Buy a VAGCOM or equivalent, or take it to an Audi dealer.

> Getting the TCMA out is a BITCH on a right hand drive car, just in
> case you care!

I know (I'm in the UK), and I do!  Done it twice now (once on each S6).  How
many screws have you got remaining that are still actually holding the
plastic cover on?

I did a write up of my early experiences with these motors.  It's on:
http://www.eveshamsquash.co.uk/audi/climate.html.

I never got around to writing up my experiences with the CC head.  I took
some photos, and sketched out part of the circuit diagram, but I've no idea
where I put them!

Paul