I have a 1996 BMW 328is with about 120K miles on it (yeah, I know, a lot of miles, but hey, it's the ultimate driving
machine, not the ultimate sit in the driveway machine). A month or so
ago, my climate control computer began to turn off intermittently --
but it would leave the AC compressor engaged. The AC light on the AC
button would remain lit, as would the air vent button (whichever one
had been last selected), but the display would be dark, and hitting the
buttons did nothing. So, you would have the AC compressor on, but no
fan.
The problem seemed to be temperature-dependent, with high temperatures
resulting in more cases of intermittent "off" events. Today, it stopped
working altogether. Nothing about this is the Bentley manual. I checked
with the folks over at BMW Central,
and they all seemed to agree that this was a problem with the Climate
Control computer. One of the board contributers pointed me to a couple
of other boards where the problem had been discussed and a fix brought
up: the The Unofficial BMW Bulletin Board and Bimmerforums.com.
Both suggested replacing a capacitor on the board of the climate
control computer. Being short on money, but having some spare time and
no fear of screwing up (I figured if I had to replace the computer
anyway, might as well give this a try first), I decided to give it a
try. This is my story.
The Tools
Here's a list of the tools that I used in repairing my climate control computer:
- Small Philips screwdriver
- A couple of small flathead screwdrivers
- Needle-nose pliers
- Wire Cutters
- Razor blade
- Radio Shack 30W Soldering Iron
- Desoldering braid
- Solder
That's it.
The Parts
Here's a list of the parts that I used in repairing my climate control computer:
- 0.47 microfarad 50 volt tantalum capcitor, about 49 cents at Fry's Electronics
A word about capacitor sizes
When I repaired my climate control computer, I
used a 0.47 uF capactitor. Now, since I've posted this page, I've had a
number of people contact me and tell me that I was wrong, that it was a
47 uF capacitor instead. So many, in fact, that I managed to convince
myself that they were right, and I updated the page to reflect my
newfound wisdom. However, I've had other people say, no, 0.47 uF is
right. Anyway, I did a little checking, and I did indeed use a 0.47 uF
capacitor.
So, if you used a 47 uF instead of a 0.47 uF, does that mean
your computer is going to blow up? I don't think so. I am not an
electrical engineer, but the capacitor here is being used as a filter
-- I would venture a guess that as long as the capacitor is larger than
a certain size -- say, 0.47 uF in this case -- the filter shouldn't
really care too much if the capcitor is bigger, even if it is a lot
bigger. Now, if this were a resonant circuit, clearly that wouldn't be
the case, but with my admittedly limited understanding of filtering
circuits, even if the right size is 0.47 uF, a 47 uF capacitor should work as well.
Like I said, this is outside of my area of expertise, so if anyone really KNOWS the answer here, by all means let me know.
Why a tantalum capacitor you might ask? Well, the directions on the other boards suggested any
type of capacitor of the correct size (0.47 microfarad) and voltage
capacity (at least 35 volts) would suffice -- the tantalum was all
Fry's had in that size the day I went, except for electrolytics, and
you've got to get the polarity correct on an electrolytic or it will
blow up, so tantalum it was. Note -- actually it has been brought to my
attention that tantalum caps are polar as well, but I've also been told
that in this filtering mode, polarity of the tantalum cap doesn't
matter. I didn't know Ta caps were polar, so either polarity doesn't
matter, or I got lucky and did it right the first time!
On the other hand, if you are dying to use a polar cap (Ta or
electroytic) and want to make sure that you get the polarity correct,
here's some info from other (more knowledgeable) owners that have fixed
their climate control computers:
"I went to Radio Shack and found that the only 47uf caps they
had were polarized. I figured that one of the connections was to the
ground plane, so I scratched off the negative leg of the other blue cap
to the left (Just above your capacitor text in the blow up view of the
square cap). I did a quick continuity check and found that the left pin
(when viewed in the same orientation of your picture) was in fact the
ground pin. In any case all this means is that a polarized capacitor
may be used, and should be oriented with the negative pin on the left.
Another way to look at it is the capacitor should be oriented 180
degrees from the other blue capacitor."
"Another happy "customer"! Worked like a charm. My only
deviation from your instructions was to paint over my work with some
clear nail polish to replace the epoxy I scraped away.
P.S. I used an electrolytic cap, because that's all that Radio Shack
had, but I think I figured out the polarity of the one I was replacing
and matched it up. Either that or polarity doesn't matter."
"Just wanted to say thanks for putting up the E36 fix. Completed on the
GF's 323, she thinks I'm a genius (thanks to you ;) I only saw one
issue: tant caps are quite polar. Regardless since the cap is used as a
filter: polarity (or non-polarity) doesn't matter"
"p.s. I used a 35v cap instead of a 50 and it seems to do the
job. If for some reason it blows again, I will follow up with an email.
"
The Repair
First thing you have to do is get the Climate
Control computer out of the car. To do that, first you have to get your
Multi-Function Display out of the way. This is very easy; put your hand
into your sunglass or whatever slot, put your fingers through the hole
in the top of the holder, and push the MFD forward to pop it out:
Yes, I realize my car is dirty. Slide the MFD forward, pop it out, and let it hang out of the way:
Now, just reach into the MFD's slot and push the Climate Control computer forward with your fingers:
If you flip the computer over, you will need to remove the two
wiring harnesses that connect it to the car. The Black one just pulls
straight out; the other one, you flip the white lever and the connector
pops out. You gotta love these BMW connectors...
Now that it's undone, get it over to your workbench, and take
out the four screws on the back. They have a Philips head, but the
screws are in tight and are pretty soft, so I ended up using a small
flat-head screwdriver to get them out. You mileage may vary:
With the screws out, you need to pop the tab on one side out
with a screwdriver, and then squeeze together the tabs on the other
side to get the front of the computer off:
Next. pop out the circuit board with the display on it:
Next, remove the fan for the AC control (I think that is what
this is, not completely sure). You might want to do this before you get
the front of the computer off, because the screws again are small and
soft and you may want to have more structural soundness to work with.
It worked for me this way, though, so it's up to you. Remove the
connector by pulling it straight out:
Next, you need to slide the main circuit board out. This is
both easier and harder than it looks. There are two tabs on either side
of the housing that hold the board in place:
I got one side popped out easily by pushing the board forward
from the back with a screwdrive while applying some pressure to the
housing. The other side was tougher -- I had to use one screwdriver to
pry away the housing while pushing from the back with the other one:
It wasn't that hard once I figured out what to do. Push the
board forward from the back until it slides out easily, and you end up
with this:
The next thing you want to do is locate the proper capcitor on
the fron of the circuit board -- it's the square blue one closest to
the big blue connector:
If you flip the board over, you can locate the two pins for the
capacitor in question by first getting into the general area, then
looking for a small surface-mount resistor -- the two pins for the
capcitor are right next to that surface-mount resistor (the screwdriver
is pointing at the resistor):
I used a razor blade to scrape away some of the laquer coating
from the pins, then used my soldering iron and a desolder wick to
remove the solder from the pins. Once the solder was removed, I was
able to easily pull the capacitor out from the front with my
needle-nose pliers (I had to rock it a bit to break away the lacquer,
but it came out pretty easily). I chased the holes with a piece of
stiff wire (probably an old guitar string) of the right diameter, then
inserted the new capacitor. A little solder later, I snipped off the
leads, and the new cap was in place:
Reassembly was the opposite of disassembly, as one might expect
-- everything went back together very easy. I popped the repaired
computer in the car, and it worked perfectly! I'll let you know if it
continues to work, but it sure looks good so far.
Total time to repair: About 90 minutes, but now that I've done
it once, I could probably do it again in under an hour easy. Total
price: 49 cents, plus tax -- I already had everything else. Even if you
have to buy everything from scratch. it would still be a LOT cheaper
than getting a new or rebuilt computer!
NOTE
If
the images don't appear in your browser, I don't know why that is
happening -- the pictures are here, and seem to work with most people.
I've tested the site with IE and Mozilla, both work fine, but I still
have some people saying they can't see the pics. Sorry about that. If
you can't see the pics, you can download a ZIP file containing all of
the pics here.
Okay, I guess I lied. It really wasn't working with Mozilla. It work
with Mozilla now, so you Netscape users shouldn't have any trouble with
the pics.
Update
Many moons later (about 25K miles), this fix is
still working fine. I've heard from >50 BMW owners from as far away
as Russia and Australia, and the fix seems to be working for all of
them.
I've also heard from people in the UK that there is some
"bloke" (would that be the right English term?) selling a PDF of this
webpage on eBay. Now, I'm not about to hire a team of international
lawyers to go after this guy for copyright infringement or anything,
but what people can do is spread the word that the info in his eBay
auction is available FREE here, and at other places that have mirrored
this site or copied it wholesale (with my permission) to another site.
Another Update: July 25, 2008
Hard to believe it's been almost 4 years since I
last updated this page. Don't really have anything new to report --
still have the car, I just went past 186,000 miles Wednesday -- and the
climate control computer is still working flawlessly. Fan stopped
working, so had to replace the resistor pack last weekend, and the
radio stopped working -- please don't bid against me on eBay, I'm
trying to get another stock head unit cheap! -- but the car still runs
good. I am still getting emails, over 200 by now from many, many
different countries and reqions of the U.S., and people seem to be
having success with the repair. I guess as long as E36 BMW's are still
out there and being driven, I'll keep the page up!
Happy driving -- I guess I'll update in another couple of years, or sooner if anything new comes up!
Last Modified: 07/26/2008 00:16:58
by Richard Swope