jstyer

Noticed last week that my defrost flap was not working...

So I yanked the defrost flap servo and opened it up. All the wiper tracks, contacts, and solder points look fine. No discoloration, no dull solder points, basically it all looks kosher. I was able to cycle the servo out of the car all the way to the stops in both directions using a 9V battery, albeit with a slight bog down in the middle of travel.

I re-installed the servo in the car in the defrost position and the ccu will close the flap, but not reopen it. I reset the servo a few times and every time the ccu will only close the defrost flap, it will not re-open it.

What do you guys think, CCU issue or servo issue? Any other things you think I could check on the servo? I'd like to cycle the flap using the CCU without the servo in place to check the voltage, but I don't have the scantool.

As always, your thoughts are appreciated!

ToreB

This is probably a CCU issue, caused by a servo fault. The cause is most probably a worn servo motor, causing short-circuit and damage to the CCU output. The Defrost servo share CCU output with both the foot well and fresh air servo, and I'll put my money on a faulty fresh air servo. My CCU DIY page have the details on the CCU outputs and how to test them with a voltmeter.
Cheers,
Tore

jstyer

Thanks Tore, I have been using your site for a while now, it's a treasure trove of information!

My fresh air flap actually seems to be working right now... So I'm not sure if that's the culprit or not. However I will definitely be taking a look at the TCA2465 to see if there are any burns or solder discoloration.

If I understand the diagram on your site correctly (Internal Connection Diagram) does that mean that whenever you turn on the defrost slider, the fresh air flap also opens? And whenever you turn the footwell slider on, the defrost flap closes?

I'm looking at outputs K6,K14 and K3,K15.

Let me know if I'm getting that right... Thanks!

ToreB

Thanks .
You are almost there. The servos operate independently, if you look closely, K14 and K15 are the ones used for the defrost servo, and K3-K16 is the fresh air servo. These two servos share K3/K15, and only one of these servos can move at a time.
If a servo is to move, both outputs are activated, either to GND or to +12V, respectively. If the defrost servo is moving, K16 will not be activated, thus no movement in the fresh air servo. K3/K15 can then be used for driving the defrost. This output could also be killed by a shorted fresh air servo motor, either by killing the +12V or GND part of the bipolar transistor output. This depends what direction the servo was to be moved when (if) it shorted.
If the fresh air servo is moving in both directions, the CCU outputs must be OK. Try connecting a different servo to the defrost output. This could be done by moving the servo connector in the trunk, but there's not much play.
Cheers,
Tore

jstyer

I'm going to continue to update this thread, so that someone may be able to reference it in the future if they have a similar problem.

I was doing some other dash work, so I removed my CCU to take a look at it. The circuit board and all the associated IC's look very good. Again, no sign of damage or discoloration... But as Tore mentions on his site, the faults in the CCU outputs can be hard to 100% identify without the diagnostic tool.

Tore mentioned in the second post above that a faulty fresh air servo could indicate a bad CCU output. After fiddling around with the system a little more, I believe I am getting an intermittent failure of the fresh air servo. Sometimes when I press the re-circulate button, freezing outside air comes blowing through the re-circulation intake. So I'm thinking that the fresh air flap is not closing all the time.

I was really hoping that this was not going to be CCU related due to the $$$ involved. But it's now looking like that is a possibility.


(RANT ON)

The sad part is that I could fab up a MUCH simpler and more reliable unit with 6 RC servos and an Arduino in about 3 hours. But some German genius decided to tie the CCU into oil cooling and the DME... When I switch to MOTEC, this CCU is going in the dumpster.

(RANT OFF)

aribop

I am having a problem with the defrost sometimes working and sometimes I guess the flaps don't open and all the air comes out through the front vents.
Can someone tell me which of the servos controls the defrost flaps?
Thanks!

ToreB

It is very seldom that the defrost servo gives up the ghost. This servo moves very seldom. I presume you have a problem with one or both mixer servos, these move all the time, as well as the fresh air servo. . See my HVAC details page.
Cheers,
Tore

aribop

Hi Tore,
will look thanks.
I see the picture of the numbered servos. Which is which?

ToreB

Thanks for pointing out my error above, I have now edited the link as well as the pictures on my page. Use the Reload button in your browser to see new pics with explaining text.
Cheers,
Tore

aribop

Thanks Tore!!!

techman1

Tore,

About your note of the defrost being used infrequently. When I do use it, at first it does not move, then it opens with a pop. I an guessing the foam at the end of the flap is causing it to stick a little. Can the flap be accessed for cleaning? I am guessing the dash cover needs to be removed?

Thanks!
O'Neal

ToreB

This seems to be a mechanical problem with the flap. If the CCU senses any hesitation in the servo movement it will stop moving it for safety reasons until reset. (>20 minutes ignition off, or disconnecting the battery)
I have never opened the air box and cannot advise. You could possibly inspect the flap with a boroscope through the mixer chamber openings. These have lids to access the pollen filters.
Cheers,
Tore

techman1

I will follow-up with any discoveries.