Electrically actuated Fresh air vent. Control module Fix

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Austintatious
Posts: 47
Joined: Tue Jan 18, 2022 5:14 pm
Location: Fort Worth

Electrically actuated Fresh air vent. Control module Fix

Post by Austintatious »

Hey everyone, I just wanted to put this here for posterity.

I have been banging my head against the wall on the electric servo actuated fresh air vent. This is controlled by the middle lever in the center AC controls. On pre 86 models the lever was moved mechanically. 86 and after there was at least an option for an electric servo instead.

This was IMHO a stupid thing for BMW to do and should have never been done. I believe I know why they did it however. I believe the goal was to automatically close the fresh air door when max A/C was selected, regardless of the center lever position.

The lever sends a resistance signal to a controller. The controller "looks" at the lever position and then drives a servo motor located on the right side of the Duct. This servo turns a shaft on which the fresh air door "butterfly" vent is mounted to. On the Left side of the duct where that shaft protrudes, there is a lever arm that attaches to a smaller arm that is on the control board. Inside that control module, mounted to the circuit board is another potentiometer that senses the position of the door.

In my case, literally nothing worked.

The motor - Part number 64111380501

In my case the motor was completely frozen up, or rather the gear train. I had to replace the whole unit completely which was a royal PITA and costly. The screws that hold it on come in from the front of the car so You must remove a semi soft plastic duct joiner to make room and even then you must work by feel.

The motor, however, can be easily tested by removing the plug and connecting 12v to it. Do not do it for long as this is a simple "dumb" motor and will run until it hits a mechanical stop. I took out my center air vents so I could see the fresh air door move, although you can see the arm on the motor move as well... If when you first apply 12v and it does not move, change the polarity as it might have already been at the mechanical stop for the direction you first tried. If it moves, good news, you don't need a new 300+ dollar motor.

The control slider - I cannot find a part number for the electric version of this lever. The Bowden cable versions are available. I spent many hours on the phone with a few BMW dealerships and despite having part numbers on the actual electrical lever, none of the BMW dealerships could find this part. I was able to test mine with an ohlm meter and found it was not working. I was however able to clean it very well with electric contact cleaner and get it functioning. If anyone knows how to locate this specific lever, please chime in because I still would like a new one.

The control unit- Part number 64111380292 -

As far as I can tell, these are no longer available. You might find one on Ebay but it will of course be used. This is a small plastic box that is held with 2 screws to the left side of the vertical air duct. You can get to it under the drivers side dash on the left side of the center console. Be very careful when removing it. The plastic lever from the door shaft is connected to a very delicate looking piece of plastic and if you break that you will be up $4!7 creek. The arm on the control unit has a little prong that snaps into a hole on the arm from the door shaft. It is easy to get off, not so easy to get back on. The working rooms is very very tight.

In my case, I opened up the case of the unit to access the circuit board by first using a screw driver to pry out the little plastic arm that engages the POT. I then worked the backing plate out. Once I had the board out, The first thing I checked was the potentiometer using an Ohlm meter. It was not functioning at all. After a good blasting with QD electric cleaner it was functioning properly.

Now the rabbit hole goes deeper. I reinstalled everything hoping that between the dash slider and pot not working and having a new motor I would be good to go. Well, the damned thing still did not work. I called an electronics expert friend and over the phone we talked about the system and did some troubleshooting. We were able to determine that the problem was indeed the control unit. So I took it back out and over to his place. On closer examination of the board we found an integrated circuit (IC) This specific IC is what drives the electric motor in either direction. It has a heat sink on it, albiet a small one. After some more testing on the bench, we determined that the IC was indeed trash. So time to find a new one.

On the IC I found the following number... TLE4201S

A replacement was Found on https://www.questcomp.com/part/4/tle4201s1/407356187

Now, that IC is a TLE4201S1, however as far as I can tell it is the direct replacement for this control unit. I do not yet have it, but will soon and will be putting it on the board and seeing if the door now functions, however I can see no reason why it should not.


I will update this post shortly once I have everything installed and working. My electronics friend also drew out the circuit for the control unit which may help someone else in their troubleshooting efforts, So I will get a picture and post that as well, it may be the only one in existence.
Austintatious
Posts: 47
Joined: Tue Jan 18, 2022 5:14 pm
Location: Fort Worth

Re: Electrically actuated Fresh air vent. Control module Fix

Post by Austintatious »

UPDATE:

The repair was a success... The fresh air vent is now functional.

As I suspected, when you select AC on, the system closes the fresh air door no matter what position the slider is in. This appears to be the reason they went with an electric servo vs the bowden cable.

There is one aspect of the system I would like to get someone to help me ascertain. If anyone has this electric fresh air door system in their car, I would greatly appreciate a simple test. I Would like to know the voltage going to the vent motor, located in on the left side of the glove box area ( have to take the upper trim part off) There is a connector on the motor leads... with it connected, I would like to know the voltage under the following conditions:

1- Middle vent dash slider in the middle position
2- Lever full left
3- lever full right
4- AC selected ON
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Electrically actuated Fresh air vent. Control module Fix

Post by TimU »

Thanks for the detailed information, this will be very useful for others following down the same path.
Thank you also for including part numbers! Very helpful.

I have my lower dash pulled apart at the moment, in preparation for an A/C overhaul to R134a.
I'll try and get some time to check if I have the same electric servo as you do and get some readings if I can.
Mine is 04/1986 Australian-delivered 635csi.
04/1986 635csi Euro spec
Australian Delivered, RHD
Austintatious
Posts: 47
Joined: Tue Jan 18, 2022 5:14 pm
Location: Fort Worth

Re: Electrically actuated Fresh air vent. Control module Fix

Post by Austintatious »

TimU wrote: Tue Mar 22, 2022 11:23 pm Thanks for the detailed information, this will be very useful for others following down the same path.
Thank you also for including part numbers! Very helpful.

I have my lower dash pulled apart at the moment, in preparation for an A/C overhaul to R134a.
I'll try and get some time to check if I have the same electric servo as you do and get some readings if I can.
Mine is 04/1986 Australian-delivered 635csi.
Tim, that would be greatly appreciated.

The issue is that, while my system is working, what we are seeing is that with the AC on OR with the ac off and the center slider positioned at either extreme (full open or closed position) the system sends a continuous 12v to the servo motor. We are concerned about this. This seems like it could either burn up the motor OR the IC on the control board that I replaced.

The control board was thoroughly checked and all the resisters on it were working as intended.

So, either there is something else not properly functioning OR the system was designed to work this way (which is dumb).

I have a few modifications in mind in either scenario. I just need to know if the system is functioning as intended.
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