[s-cars] No heat diagnosis please

[Vincent Frégeac]

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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