Subject: E34 microfilter
Finally looked up my notes on microfilter replacement for my 9/91 E34 M50 5sp. (it has a gray tint). This is from my notes and memory (1 year later) and revised with comments by Dan Quicker ('95 540ia). If you find any errors or differences from our cars, please e-mail.
Another digester said on this: "In response to the 1990 E34 owner who couldn't find the fresh air microfilter- there isn't any. The BMW microfiche says the E34 started using microfilter beginning in 6/90 (this is wrong) - they began using the filters in 11/90."
Working somewhat from Chilton (just short of useless for this job) and mostly from BMW fiche:
1) Remove glove box by removing the retainers holding the strap and gas strut (if present) from the sides of the glove box. Lying on the floor, loosen and release the latches for the rear hinges. Dan says "Glove box is now sitting on your head."
2) Remove the carpeted panel on left side of pass. footwell. There should be a plastic cover over the screw head - remove it carefully. On Dan's 540, the carpeted panel was screwed to a gray mount that is removed by pinching the mount and sliding it out. This mount would have been in the way when you slide the filter out in step 6.
3) Remove the black cover on left side of glove box. (On this, the fiche has the wrong picture in Sec. 64-31/2 but I believe Fig. 2 of Sec. 64-31/1 is correct.) Remove the small duct going to the RHS of pass. footwell. On the 540, the black cover and the RHS footwell duct should be removed as one piece. On the '95 540 there are 4 screws and this sounds like what I remember for my '92:
a)1 holds the top of the black cover to the dash.
b)2 secure the duct behind the glove box hinge mounting bracket. On the '92, these easily fall down in between the bracket parts - it's hard to retrieve them from there!
c) 1 well hidden screw holds the duct directly above the 90 degree bend it makes from the console to the footwell. It is on the top side of the duct.
Turn the assembly out of the way. (The wires to the flashlight that don't have to be removed.)
4) On the '92, remove the wires for the HVAC control unit (I believe that's what it is) at very front & bottom of the console, right next to the fire wall. Wires have a v nice, arguably over-engineered, connector - lift the lever up and the plug automatically comes out.
Release the clip and pull out the control unit. Dan says that on the '95 540, you can leave the wires attached and just set the unit aside - pick your poison.
NOTE: Over the AC coil and heater core, there is a black cover with 7 T15 screws. The microfilter's not under there! You don't have to remove it - beender dunyat (see step 3 about wrong fiche picture.)
5) Down further & recessed (toward the center line of the car) is a small funny shaped (tall and thin) white cover (on mine) with 1 or 2 screws (T15 I believe). The microfilter is under there. I think you get it loose and then have to rotate a lever to get it out.
On the '95 540, Dan says the white cover is right next to the control unit. It is held with 1 T15 screw and a cam lock lever at the top. Loosen the screw, Turn the camlock counterclockwise. Remove the White cover. The filter is right behind it. As you can imagine, the white cover is as tall as the filter (5"?) and about 1 1/2" wide.
6) Pull the filter out. While your there, clean out any junk in there that you don't want to blow out of the center vent and into your face. (Leave the junk that you do want blown into your face.)
7) Trivial Step: Assembly is reverse.
Took me ~2 hours first time because of the brevity of Chilton and the error in BMW fiche. Should be a 30-45 min job 2nd time.
Thanks to Dan, Good Luck, & YMMV,
E34 M50 5sp US A/C - I've read Canadian AC cars may be different.