[s-cars] No heat diagnosis please

Tue Jun 19 07:48:04 EDT 2007

Bad connection around the plug is the first thing that comes to mind. Short
circuit or high drag on the motor (excessive current), both switching the IC
that control the motor voltage in protection mode could be another reason
for no voltage.

I would disconnect the servo, wait a few hours, or a full day, and test for
voltage again without the servo then with the servo connected again. This
will tell you if the problem is repeatable (bad connections rarely are) and
if it’s related to the servo.

Vincent.

  _____  

De : Sam Clarkson [mailto:sam at edgetoedge.co.nz] 
Envoyé : 19 juin 2007 00:17
À : Vincent Frégeac
Cc : s-car-list at audifans.com
Objet : Re: [s-cars] No heat diagnosis please

Thanks Vincent

I've had a play around and managed to get everything working fine, then I
put the TCMA back in and nothing!

Now I have no voltage to the TC motor. But there was voltage before.
Potentiometer reads fine.

Any ideas where the next point of weakness might be, I haven't touched the
main head unit yet, I guess a bad plug connection there might be an option.

Any swappers are many many km away.

At least I've  got the lever manually over on the hot position now till it's
all sorted.

Sam Clarkson

On 19/06/2007, at 2:30 PM, Vincent Frégeac wrote:

Hi,

I would start with voltage to the motor. Testing is fairly easy once the

servo (TCMA) is out:

- Open the servo but leave it connected, remove the motor without

disconnecting it (for easier access), move the arm in midway position, clip

the voltmeter probes to both wire on the motor, turn the start key to on (no

need to start the engine) and set the temp to LO. Check if there is voltage.

Then set the temp to the highest temp and check if the voltage reverses.

Testing the potentiometer is easy too:

- Disconnect the servo, open it, remove the center gear (the gear that pop

off by itself) then use a voltmeter to test the resistance between the left

or right post and the center post. Make sure the resistance vary smoothly

when you turn the arm.

If there's no voltage on the motor, I would first try to swap a known good

HVAC control unit. If you don't know any one close with either a C4 A6, a C4

S6 or a 90V6, try to find one in a junkyard. There rarely fail so you should

eb able to have one for very cheap. Use this write-up for the HVAC unit

swap: http://www.audifans.com/twiki/bin/view/Audi/ConsoleFrontC4, only the

steps 3 and 5: A 10min.job including the beer at the end.

If the potentiometer doesn't work well, or not at all, turn the arm fully in

one direction (the direction is irrelevant as long as you turn it fully so

it doesn't contact the center section) then slide a 400 sand paper, sand up,

between the contactor and the potentiometer to clean the contactor. Use only

a very fine sand paper or you'll make the contact surface rough and it will

destroy the resisting strip in no time.

Sorry, no idea how to reset the HVAC codes without a VAG-COM.

HTH

Vincent.

-----Message d'origine-----

De : s-car-list-bounces at audifans.com

[mailto:s-car-list-bounces at audifans.com] De la part de Sam Clarkson

Envoyé : 18 juin 2007 20:20

À : s-car-list at audifans.com

Objet : [s-cars] No heat diagnosis please

Hi all

93 S4

No Heat, I pulled the codes; 08.7 temp regulator flap sporadic block  

and 11.7 central flap sporadic block.

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.

Any advice as to what's next to test.

The potentiometer? How?

The supply to the TCMA? How?

How do I clear/reset the codes?

Getting the TCMA out is a BITCH on a right hand drive car, just in  

case you care!

Sam Clarkson

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