MyE28.com

To move fresh air into the cabin of my '86 535i I recently installed a set of SLS Gullwing Doors found at a local yard. However, South Florida's weather is very unpredictable as you can see, so opening the doors while driving has proven to be NOT a good option. I could mostly use the E28's fresh ventilation system. Problem is, the bastard doesn't work! I mean, the AC system seems fine as a whole when the blue button is engaged, both Cold/Heat.

But if I pull or disengage the AC's blue button to get Fresh Air through any vents inside the cabin I only hear the blower motor running but NO air fresh, conditioned or otherwise comes out through any vents, no matter the fan speed I select. And if you are still interested: Yes, I have played with any of the three knobs (pictured below) to the 'open air' right side trying to get fresh air flowing through but I think only twice it worked, but because this is an E28, obviously it ceased to WORK.

Bentley's useless regarding any ventilation topic and here in the Forum I believe never read a post regarding how to solve the lack of fresh air flow, but mostly about heater problems. I just want to be able to run fresh air without to resort to any Gullwing doors or other silly and unconventional methods. Cannot afford, need or want either a SLS or any type of convertible. So seriously, can you please tell me what do I have to remove from the ventilation system in my car and if I find it is at fault, have it replaced it in order get fresh air flowing? Hey, hey, no silly electric fan jokes options Thanks!

The middle slider should open the fresh-air flap, which is controlled by a solenoid. My first guesses are that either the middle slider's electrical connector has come loose/fallen off/corroded, the electrical components in the middle slider have failed OR the solenoid that controls the flap has failed.

duggi wrote:The middle slider should open the fresh-air flap, which is controlled by a solenoid. My first guesses are that either the middle slider's electrical connector has come loose/fallen off/corroded, the electrical components in the middle slider have failed OR the solenoid that controls the flap has failed.

Well, thank you so much, this is really helpful! Would figure #5 in this diagram be said solenoid?
http://bmwfans.info/parts-catalog/E28/E ... actuation/

I'm not sure if 5 or 12 is the solenoid, but here's a diagram from Shawn D. showing E28 air flow:

#7 & #9

http://bmwfans.info/parts-catalog/E28/U ... wer/#pos_7

harrypalmer wrote:

duggi wrote:The middle slider should open the fresh-air flap, which is controlled by a solenoid. My first guesses are that either the middle slider's electrical connector has come loose/fallen off/corroded, the electrical components in the middle slider have failed OR the solenoid that controls the flap has failed.

Well, thank you so much, this is really helpful! Would figure #5 in this diagram be said solenoid?
http://bmwfans.info/parts-catalog/E28/E ... actuation/

The solenoid isn't in this image and I'm not exactly sure where in the car it's located...I took a browse through realoem and can't find it, someone else may know where it is (my car's an '84 and is all cable-controlled rather than solenoid, so I'm not very familiar with the later setup). Part #5 in your image is the slider - when you take things apart and look behind there, the middle (fresh air) slider should have an electrical connector on it, make sure it's making a solid connection (that'd be your EASIEST place to start). I grabbed a quick pic from eBay and circled the connector I'm talking about:

demetk wrote:#7 & #9

http://bmwfans.info/parts-catalog/E28/U ... wer/#pos_7

It's also possible that the stepper motor #7 that controls the flap has come loose.

demetk wrote:

demetk wrote:#7 & #9

http://bmwfans.info/parts-catalog/E28/U ... wer/#pos_7

It's also possible that the stepper motor #7 that controls the flap has come loose.

I knew someone would know where that lived!

The solenoid is kinda buried near where the top of the glove box meets the center console. The solenoid mounting screws work themselves loose over time and allow the solenoid to come loose. If you can access it, tightening the screws usually gets the fresh air solenoid back into action.

You guys keep referring to it as a solenoid, but it really is a stepper motor isn't it?

waynet1 wrote:You guys keep referring to it as a solenoid, but it really is a stepper motor isn't it?

You are correct.

Man I got nothing. With an 85, I have the old style with a bowden cable handling the flap for the fresh air vent. Just so far behind the times all in one model year. GLWYR.

Blue Shadow wrote:Man I got nothing. With an 85, I have the old style with a bowden cable handling the flap for the fresh air vent. Just so far behind the times all in one model year. GLWYR.

So far behind? More like the better, more reliable system. Reportedly they put the motor driven flap in there because people were too stupid to close it when they turned the A/C on. If so those people should be driving a different car, it's not that difficult.

You know the engineering saying, if it still works it's not complicated enough yet...

Mike W. wrote:
So far behind? More like the better, more reliable system. Reportedly they put the motor driven flap in there because people were too stupid to close it when they turned the A/C on. If so those people should be driving a different car, it's not that difficult.

The upgraded the car with the non-functional top vent. Poor stupid people couldn't enjoy their cars properly. That's ok, now those same people's major complaint about their car is connectivity, nothing to do with what a car is supposed to do.

waynet1 wrote:You guys keep referring to it as a solenoid, but it really is a stepper motor isn't it?

Saw this a while back as my daughter asked -"What is that picture doing in Wayne's car, Is that Wayne?"
Hey thank you for your take. You need to get a E28 again and bring back one of these

duggi wrote:

harrypalmer wrote:

duggi wrote:The middle slider should open the fresh-air flap, which is controlled by a solenoid. My first guesses are that either the middle slider's electrical connector has come loose/fallen off/corroded, the electrical components in the middle slider have failed OR the solenoid that controls the flap has failed.

Well, thank you so much, this is really helpful! Would figure #5 in this diagram be said solenoid?
http://bmwfans.info/parts-catalog/E28/E ... actuation/

The solenoid isn't in this image and I'm not exactly sure where in the car it's located...I took a browse through realoem and can't find it, someone else may know where it is (my car's an '84 and is all cable-controlled rather than solenoid, so I'm not very familiar with the later setup). Part #5 in your image is the slider - when you take things apart and look behind there, the middle (fresh air) slider should have an electrical connector on it, make sure it's making a solid connection (that'd be your EASIEST place to start). I grabbed a quick pic from eBay and circled the connector I'm talking about:

Thank you Demetk (Jim) I really appreciate you've taken the time since I am visually oriented it facilities my search. Like duggi suggested, I will start with the middle slider, and the connector you've pointed out.

Kyle in NO wrote:The solenoid is kinda buried near where the top of the glove box meets the center console. The solenoid mounting screws work themselves loose over time and allow the solenoid to come loose. If you can access it, tightening the screws usually gets the fresh air solenoid back into action.

As usual, awesome advice. Thank you Kyle.

Thank you John in VA and by default Shawn D; I've never really understood that diagram but now I do. I guess I have my limitations

Also, thank you both Mike W and Blue Shadow. I will get my hands on this next week and share any fresh air result updates. Much appreciated.

Jack

Kyle in NO wrote:The solenoid is kinda buried near where the top of the glove box meets the center console. The solenoid mounting screws work themselves loose over time and allow the solenoid to come loose. If you can access it, tightening the screws usually gets the fresh air solenoid back into action.

This was the problem I had and this thread helped me: http://www.mye28.com/viewtopic.php?f=3&t=27613&hilit

Karl Grau wrote:

Kyle in NO wrote:The solenoid is kinda buried near where the top of the glove box meets the center console. The solenoid mounting screws work themselves loose over time and allow the solenoid to come loose. If you can access it, tightening the screws usually gets the fresh air solenoid back into action.

This was the problem I had and this thread help me: http://www.mye28.com/viewtopic.php?f=3&t=27613&hilit

There you (I) go... Air 'Flapper'. No wonder I couldn't find anything in my research. Karl Thank you!
Jack


I guess I should continue this: http://www.mye28.com/viewtopic.php?f=3& ... 6#p1379936 here instead. Anyway, is it possible to tighten or removing the Flapper Motor screws without dismantling the dashboard? Is there any other solution please?

Resurrecting this thread. The info above has been very helpful, but I still can't get the center vents to react to the center slider.

i think these are the two diagrams from RealOEM and the ETM that are relevant.





My problem: No air from any of the center vents or the vent at the top of the dash.

Car: 1987 535is, US spec, but with a "working" dash-top center vent

I dug under the dash to check & test stuff, and here's what I found:
- Stepper motor is mounted firmly with all three screws tight & in place. Armature of the stepper motor is properly attached.
- Wires going to the back of the center slider are present & accounted for and hooked up
- Fresh air door control unit ("FADCU", #9 in the Real OEM diagram) is present & accounted for and hooked up to the incoming 7-pin connector
- BUT ... armature of the FADCU was detached

First step was to reattach the FADCU back up to the armature. Done.

Started testing:
- Stepper motor works fine when energized to a 12v poser source. Hook it up one way, motor steps in one direction, reverse the polarity of the incoming power and it steps the other way. ANd when doing so, I can open of close the fresh air door and get or shut off air from the center vents.
- Checked all the connections at the slider ... I get a nice smooth variable resistance when I hook a DVM from pins 1 to 3. It's nearly infinite ohms when I slide to the left, closer to zero ohms when I slide to the right. Pin 2 has good continuity to ground.
- On the FADCU, I check the incoming leads: continuity to the stepper motor (pins #7 and #4), continuity to the center slider (Pins #2 and #3), solid connection to ground (#6), 12v+ at pin #5, AC on input works fine (pin #1, 0v when AC is off, 12v+ when AC is on)

Based on some testing, here's what I think the system is supposed to do:
- User slides the slider in one direction.
- That changes the voltage input to pins 2 and 3 at the FADCU
- The armature of the FADCU is hooked up to the fresh air vent. The position of the armature controls a potentiometer inside the FADCU, which "tells" the FADCU what position the fresh air vent is in.
- If the slider voltage (from the potentiometer in the slider) isn't matched to the voltage registered by the FADCU based on the position of the armature-potentiometer, then the FADCU moves the stepper motor accordingly.

So, I think I have a bad FADCU. Thoughts? Anything else I should try before I go chasing a replacement off of a wreck?

Test the stepper motor with 12 volts in both directions. My controller was bad so I just used a window switch to temporarily control it.

Yup, did that. Works great.

jhh925 wrote:Yup, did that. Works great.

Oops, now I see it.

So my center vent is working again. It was the "fresh air door control unit" (hereinafter, the "FADCU").

This isn't earth-shattering, but I figured I'd document my process in case it's helpful to future generations. A lot of this is regurgitation of stuff above, and I'm only trying to organize it for trouble-shooting & repair purposes.

The center vent operation relies on at least three components:
- The stepper motor at the passenger's left foot, just inboard of the glove box (#7 in the RealOEM diagram above)
- The center vent slider control in the AC control pod (called the "fresh air door control potentiometer" in the ETM above)
- The FADCU attached to the ventilation ducting on the driver's side, essentially just opposite of the stepper motor (in fact, the FADCU and the stepper motor are connected to the opposite ends of the rotating shaft that passes through the central vent box and that operates the fresh air vent inside that box - the stepper is on the right side of the shaft, the FADCU is on the left side) (#9 in the RealOEM diagram above)

Based on the failure modes described above, if you're not getting central vent air, or if you're getting it but you can't turn it off because your central slider isn't able to close the vent, then do this:

1. Check your stepper motor. As noted above, drop the glove box, remove the hard plastic cover that's just inside of the glove box. Common failure modes are: (i) screws are loose, (ii) motor has failed, (iii) armature coming off the motor has fallen off or broken.
2. Check your center vent slider control. As noted above, loosen the radio pod and check that the 3-pin connector to the slider is in place.
3. Check your FADCU. This one is tough to access. Remove the kick panel. Look up alongside the ventilation system between the steering column and the ventilation system. There's a box that looks like a tall relay. Under that is a multi-pin connector. Slide them both out of their bracket. You should now be able to see the FADCU. It has a 7-pin socket going into it. The FADCU has a three-link armature connected to the same shaft that connects at the other end to the stepper. Before you remove the FADCU, you will only be able to see two of the arms. In any case, confirm that you see a tall white arm coming up from the FADCU connecting to a shorter white arm that comes down to the vent shaft.

Suggested testing steps:
1. Test the stepper motor. Unplug it from its connector. Apply 12v one way, then the other way. With one polarity, it should rotate 180 degrees one way, and with opposite polarity, it should rotate 180 degrees the other way. Confirm that when the motor rotates, the armature is moving vertically up and down, and in so doing it rotates the shaft that goes into the center ventilation box.
2. Test the slider. Confirm that the 3-pin plug is attached properly. Remove the plug. Attach an ohm-meter between pins 1 and 3. Move slider far left, you should get ~infinity ohms (vent closed). Move slider to the far right, you should get a very low number, something approaching 0 ohms (I think I got 10 ohms)
3. Test the wiring.
- Test continuity of the wires from FADCU to stepper
- Test slider ground (slider pin 2)
- Test FADCU connection to ground at FADCU pin 6
- For the next two tests, make sure the 3-pin connector to the slider is in place
- Turn ignition on, test for 12v+ at pin 5 going into the FADCU
- With the ignition still on, make sure the AC button is off. Confirm 0v at pin 1 into the FADCU. Turn the AC on. Confirm 12v+ at pin 1 into the FADCU.

If your center vent doesn't work but all the tests above are good, then your FADCU is likely bad. They're still available new for $120-ish, but if you can find a part-out I'd guess the part is still there, and probably cheap. In my case, the FADCU armature had been disconnected, and my theory is that since the input shaft wasn't moving the potentiometer in the FADCU, the FADCU just burned out trying to move the stepper.

Stepper motor with armature shown pointing up from the far side of the stepper:



Three-pin connector going into the slider control. From this view, the pins are 1-2-3 reading from left to right



FADCU with armature and socket in place. The longer link coming off the back of the FADCU is obscured in the shadows. The shorter link is visible in the foreground attached to the vent shaft. From this view, the pins are reading 7-6-5-4-3-2-1 from top to bottom. Removing the FADCU, reattaching the armature, and putting the FADCU back in place will be ... challenging.