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Blower Control Repair w/ pics!

Posted: Thu Mar 16, 2006 4:21 pm
by bfons

Posted: Thu Mar 16, 2006 5:01 pm
by horsetan
:idea: :idea:

Excellent :!:

Posted: Thu Mar 16, 2006 7:07 pm
by UKDaveJ
Brilliant!! :D

Posted: Thu Mar 16, 2006 7:10 pm
by Djangoz200
If anyone wants clarification on anything in this article feel free to pm me as the original author (Andrew K) :)

Posted: Thu Mar 16, 2006 7:14 pm
by DC
great - I have this problem now too ...

Posted: Tue Mar 21, 2006 3:08 pm
by livnlyf1s
thanks for the info. still not sure if i am capable of attempting this but maybe in the future i will "see if i've got the minerals". def. would like to get the variable blower working again. the other day i was puttzin' around in the car and started playing with the a/c fan and noticed that the variable motor works. that was good to know/ find out. i thought it was the same fan motor for both. it wasn't all or nothing; i'm guessing my problem is just the resistor for the regular fan. SO my blower is all or nothing when trying to use with the heat and it is variable when using the a/c but the a/c doesn't blow cold.

Posted: Tue Mar 21, 2006 4:10 pm
by Djangoz200
If you have variable fan on a/c blower but NOT heater blower, conventional wisdom says that it's the transistor behind the blower motor under the bonnet that's faulty, not the fan control.
Remove the four screws holding the fluted black cover in front of the windscreen in the area where the wiper motor and intensive fluid reservoir are found. Then unclip the rounded black covers over the fan cages. Undo the metal retaining clip around the blower motor itself and you should be able to lift it out enough to see the transistor mounted in the back of the blower housing. It's on the drivers side on a Euro so I guess that's passengers side for US.
It's held by two nuts and bolts and is a bit fiddly to get at. Once it's out just unsolder and replace the transistor (2N3055 or similar), put it all back together and you should be fine.
Do check that the bearings are ok in your heater blower though as if they are very tight they might be stopping fan from rotating unless you give it full power.

Posted: Wed Mar 22, 2006 7:30 pm
by livnlyf1s
thanks. will look into it this weekend. sounds simple enough. sounds easier than irginally thought.

Posted: Mon Jan 14, 2008 4:23 am
by Chris Wright
The above link to the Word Doc. seems to be dead. I had previously downloaded it, so I saved it as a PDF file and uploaded it to the forum again.

Posted: Sun Jul 27, 2008 7:40 pm
by Sixracer
Thanks for uploading that document again!

One rather preliminary do I remove the blower controller?

For Sixracer

Posted: Wed Aug 20, 2008 1:47 am
by Hefeweizen
Repairing Blower and Temperature Controls - Todd Kenyon <[email protected]

Here I will try to give as complete an account of possible of a common repair on E24s, probably early E28s as well. Mine is an '84, but much of this should apply to any models with a continuous fan speed dial (as opposed to a 4-position rotary switch) and a rotary temperature dial. Don't be overwhelmed by all the detail - it will make sense as you are doing it. This is not a difficult repair. Took maybe 2 hours with a lot of trial and error. Thanks to all those who supplied info, especially David Hoerl and Rick Sparks (Big Coupe Group).

The problems:

Blower fan (the one located in front of the firewall, that can be accessed by removing sheet metal panel under the hood immediately in front of windshield) only operated on FULL BLAST, regardless of whether air conditioner was on or off. Around the same time, my temp control became difficult to turn, and then became way too easy to turn when I, ahem, tried a little force. These are unrelated problems, but convenient to repair together.


The fan speed control contains a NPN transistor on its internal circuit board that sooner of later frys. It still works on full speed because the control activates a leaf switch at full blast that bypasses the control circuitry and supplies full V/A to the fan.

The temp control has a potentiometer (rotary resistor) that siezes up over time. The dial is connected to the pot with a plastic three-piece universal joint which is easy to break if the pot siezes and you force the control. I recommend lubing this control even if it isn't giving you problems yet.

Parts needed:

from Radio Shack, get a TIP3055 NPN silicon transistor (#276-2020); cost is $1.59, stock item. Get a can of stereo control cleaner/lubricant spray for the temp control.

From BMW: nothing, unless you need to replace the universal joint - I assume you can buy these, but am not certain.

Removing dash panel:

The ventilation control panel consists of the trim panel you see, and a mounting frame attached to the back of it which holds all the controls. To remove the panel, use a small screwdriver to pop out the 4" x 3/4" black plastic strip between the gauge cluster and the ventilation panel. Behid this are 4 screws, 2 of which hold the left side of the vent panel (remove). Then use same tool to carefully pry out hazard, AC, and defrost switches (prongs that hold them in are on top/bottom of switch), pull them out of panel, and unplug wires. Now you can see a screw hiding above the hazard switch and below the AC switch, inside the holes - remove. The panel will now pull out from the dash, but only a short way due to wires and Slider cables. Pull the knobs off the two rotary controls, and the three vent sliders (careful, dont break them, there are three pieces for each slider knob - you should be left with flat metal tips holding small leds that light the knobs) Also carefully pry off the small plastic, switch-sized panel that has a diagram of the slider settings for defrost on it. Now you will see 2 screws behind this panel, and 2 behind the blower speed knob. Remove these and you can remove the trim panel from the mounting frame, but be careful of the two small lightbulbs inserted above each rotary control (they just pull out). Now you have the frame with attached slider mechanisms and rotary controls. Unplug all wires. To free the frame, you last need to remove the cables from the slider mechanisms. These are colorcoded R,B,G so you can reattach them properly. Removal is pretty self explanatory once you see them. First remove the spring clips that hold cable housings to frame (just pry w/ screwdriver - careful, they will fly away at high velocity, probably into the dash amidst a tangle of wires- ask me how I know) Then manuever that cables so you can pop the ends of the pins. NOW IT IS FREE! Really not as bad as it sounds, it will be clear as you are doing it.

Fixing the controls:

Temp control:

Each rotary control is mounted to the frame with small screws. You should see the white plastic universal joint for the temp control - careful you don't break or lose this - the middle piece is a tiny cube about 5mm square. I pried the back off of the control and pulled out the circuit board so I could spray the cleaner/lube directly into the slots in the side of the pot. Freed it right up. I had broken parts of the Ujoint, but it was mostly intact and I didn't have a new part, so I reassembled it and wrapped it with electrical tape. May not hold, but so far ok. If yours seems broken before you remove the panel (knob moves freely, NO resistance) try to get the part first. Thats it for the temp control. Fan speed control: Remove the speed control's frame screws, and pry the back off it. You'll immediately see the circuit board with the transistor. I took the board out, unsoldered the old NPN, and resolderd the new one in the 3 holes. Rick just cut his old one off and soldered new one to the cut-off legs of his old NPN. Either way. The old NPN has its integral heat sink riveted to the board - I left it there (just the metal plate - pulled the old transistor off it) and just left the new NPN jutting out from the board at an angle. Careful when you reassmble the control, as the leaf switch has to be mounted properly, and the shaft of the control has notches and projections that interact with the switch and a spring - sounds nasty, but its obvious how it should go once you see it. Done!

At this point I reattached all wires without reassembling the panel and tested it. BINGO! Works fine. Now more or less reverse the process to reassemble. Don't forget to plug in all wires and reinsert lightbulbs. Make sure that the black plastic collars on the ends of the vent cable housings are held underneath the clips. May take a little wrestling.

On a related note, its probably a good idea to lube the bearings of the blower fan (use heavy motor oil of diff fluid) at this time. The increased load from a poorly lubed fan might be what causes the transistor to blow - mine actually appeared burnt.

Whew! My typing finger hurts. Good luck, happy to answer any questions.

Posted: Wed Aug 20, 2008 3:19 am
by C-Fade M-Tech
yep! I just did this (But I replaced the whole board that was already repaired 8) ) Mine works great! and it is an EASY repair and WELLLLLL worth it....

Posted: Sun May 20, 2012 3:59 pm
by Carlp336
cant seem to locate AC blower transistor on my early unit... found the heater one and fixed it.. but hte ac is only on high too..

Posted: Sun May 20, 2012 6:16 pm
by Carlp336
Carlp336 wrote:cant seem to locate AC blower transistor on my early unit... found the heater one and fixed it.. but hte ac is only on high too..
found it

Posted: Sun Jun 21, 2015 2:14 pm
by ramp
Question, we are digging behind the dashboard correct?

Posted: Wed Jun 24, 2015 3:27 am
by Noct
ramp wrote:Question, we are digging behind the dashboard correct?
Basically yes. The blower fan he recommends lubing is accessible from under the hood, after removing 6 screws mounting the panel between the firewall and the windshield.

Re: Blower Control Repair w/ pics!

Posted: Sat Aug 27, 2016 7:34 pm
by nerdorama
Hi everyone,
Just got a 6'er, 1989. I have a blower problem that doesn't seem to be quite one of the scenarios that have been mentioned. The dash speed control works fine for the AC blower through the variable range and at full. When I switch off the AC, I get nothing on the heater blower anywhere in the control range. I can hot wire the blower and it runs fine which tells me the changeover relay is working since I just jumped the plus connection quickly to the battery. Blower runs fine and quietly, i.e., not bearing issues etc. I've got the blower control schematic from the troubleshooting manual. I'm guessing it's a wiring/connector issue somewhere since the AC blower works fine at full speed which is also shown as being direct connected to the positive of the heater blower. I also imagine that I have a transistor problem since I don't get anything in the variable speed range either. I don't get any voltage at the blower positive terminal. Are there some connectors from the speed control under the blower or inside the dash that might allow the AC blower to work but prevent voltage from getting to the heater blower? I don't really want to dig into the dash until I have an idea of where I'm going.

Re: Blower Control Repair w/ pics!

Posted: Wed Aug 31, 2016 5:04 am
by nerdorama
Looks like I have a blown transistor. It's funny but it also doesn't run on high where the transistor is supposedly bypassed for full voltage. The hot wire to the blower only goes to the transistor module so maybe it really isn't wired that way and it just puts full voltage on the base of the transistor. Anyway I should have a new transistor by Thursday and will see what happens.
Thanks to all who have posted info about this problem.

Re: Blower Control Repair w/ pics!

Posted: Sat Sep 17, 2016 10:54 pm
by nerdorama
It seems that the blower control on the dash doesn't really bypass the transistor, just the potentiometer part. It all goes through the transistor, which was bad, and now I have full function including high. Thanks to everyone/anyone that has posted about this problem and the solution. Ten dollars in parts and I have air again.

Re: Blower Control Repair w/ pics!

Posted: Sat Oct 22, 2016 7:29 pm
by ramp
Great write up. First cold Fall day here in Connecticut. Picked up transistor at Radio Shack and fixed the switch. Ebay had a used one for $90. 2 bucks from Radio Shack, priceless....

Re: Blower Control Repair w/ pics!

Posted: Sun May 07, 2017 7:01 pm
by stugilmour
Half way through this job with everything removed and the transistor ordered. To add a few details to the excellent dash opening procedure above (my car is a 1987 M6, which probably accounts for some differences):
  • I damaged the vertical plastic strip located between the heating panel and gauge pod. I am pretty sure I can fix the issue with double-sided tape. The three plastic push pin retaining studs are located on the right side of the strip, so perhaps try prying it free from the right side to avoid breaking the studs? I prayed from the left side and probably angled the pins too far; all three sheared off flush with the back of the plate.
  • Make note of the positions of the four screws under the plate. Two have washers and two do not.
  • The two retaining screws on the right side of the heater control panel are a bit difficult to see initially, particularly with the switch connectors in the way. Both screws are vertically angled toward the switch holes, and are the same size & colour as the two screws behind the pictogram plate. Recommend having a magnetic pickup tool to hand to unscrew the last threads and avoid loosing the screws upon removal.
  • My 1987 heater control only had two cables (colour coded red and green as noted above). The middle slider control uses a linear rheostat on a small circuit board. Presumably one more electrical connector to manage, but no big deal.
  • I had three black zip ties retaining the loom below the heater control. I found I needed to snip them off to be able to position the heater controls for cable removal.
  • The cable retaining clips (at the end of the cable sheath) do want to take off when released. Consider using the magnetic pick-up while prying them off. Note the flat part of the clip goes to the bottom. Once the sheathing is released the cable end is rotated about 30 to 45 degrees to release it from the slider mechanism.
  • Removing the three slider knobs was reasonably easy by gently prying with a small screwdriver. The small LED's stay attached to the metal slider arms; didn't initially look like they would fit through the slider slots, but they do. I took a picture of the attached knobs to make sure I install them correctly; they have a angled back face.
  • The various electrical connectors look fairly straightforward to re-attach; most only fit one place. Make note of the two loose female spades on the fan control knob. There seems to be three similar flat connectors that could be connected out of order, but I expect they don't matter; looks like they are for the slider knob LED's.
  • As I may have a longish wait to get my replacement transistor, I inserted all of the screws where they go, re-attached the switches, re-fitted the slider knobs, etc. so no loose parts to loose and assembly will come back to mind.
  • There appear to be several versions of the required transistor available on eBay, Amazon, etc. The Source does not carry the favoured Radio Shack item and will not order it. However, I was able to get a NOS Radio Shack transistor on eBay by searching on the RS part number. I expect the other replacements will work, but they did not have the same heat sink plate as the RS item.
I was kind of dreading this job, but so far it is pretty straightforward and satisfying. Hopefully the part sourcing, soldering, and re-assembly go as easily. Plan to run a vacuum cleaner through the ducting while stuff is apart. :D


'87 M6 (Canadian spec, no rear seat ice box)

Re: Blower Control Repair w/ pics!

Posted: Tue May 14, 2019 1:13 pm
by gte619n
Hey fellas, looks like Digikey no longer has the old ST part.

I'm going with this ON Semiconductor MJE3055TG from Mouser. I'll follow up after the fix...

Re: Blower Control Repair w/ pics!

Posted: Tue Aug 13, 2019 2:03 pm
by gte619n
... that didn't work ... more research needed.

Re: Blower Control Repair w/ pics!

Posted: Mon Dec 16, 2019 4:39 am
by baders
You should look up this transistor;


It is rated at 30a thus twice the current carrying capacity of the original.

Re: Blower Control Repair w/ pics!

Posted: Tue Jan 14, 2020 11:19 pm
by sansouci
Don't forget the silver heat conductive paste to bed the transistor for better heat dispersal.