Heater fan inop

Post your E12 technical questions and comments here. Please, no off-topic posts.

Moderators: Mike W., Pierre

Post Reply
User avatar
maybeillbuyit
Posts: 142
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Heater fan inop

Post by maybeillbuyit » Sun Apr 21, 2019 1:05 am

The heater and AC fans dont work in my 77 530i. It worked a bit when I first got the car but now that the car is operational the fan doesn't do anything. Electrical diagnosis is really my weakest skill. I've read Peters excellent write up in the FAQs for the heater fan control re&re to get rid of the sticky gummy control ring issues. But my control ring spins nice and smoothly so I'm thinking it may be something else. I don't see anywhere on the forum or web anything about a resistor like the e28 has, is there one on the e12? Or maybe some other well known problem that may affect the blower motors function? I suppose it could be the control ring needing to be dismantled and cleaned but I thought I'd ask here first before tackling that. Thx Dave . All the fuses are in good shape and none are blown
1977 530i another project
1979 635csi Euro "project"
1987 635csi

User avatar
528i-1981
Posts: 130
Joined: Wed Feb 07, 2018 5:50 am
Location: Boston North Shore, MA

Re: Heater fan inop

Post by 528i-1981 » Mon Apr 22, 2019 2:39 pm

Hi Dave - maybe this will help, maybe not. Electrical gremlins have myriad causes. The center console plug (8 pins I think, it also connects to the rear defogger switch) has a green wire with a brown stripe that brings power to the blower motor (that's the way it is on the 81 528, and I assume the same for you). I believe that the dial control with the clock changes the resistance through the ground, and that's how you get different speeds with the blower. If you can probe that GRBR wire (with the key on) against ground and get a voltage (12V) then at least you know the blower is getting power, and therefore that the ground is the problem ... and therefore likely the dial control will likely be involved. If you don't get a voltage, well then maybe it's a loose connection or a problem in the fuse box. That part of the circuit is very simple on the schematic. Good luck!
(oo=00=oo) Eric
1981 528i Manual

User avatar
maybeillbuyit
Posts: 142
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Re: Heater fan inop

Post by maybeillbuyit » Thu Apr 25, 2019 12:41 am

OK thx for the tip Eric. I'm sure I probably need to just remove the whole unit and clean the rotating dial properly.
1977 530i another project
1979 635csi Euro "project"
1987 635csi

User avatar
Mike W.
Posts: 2405
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Heater fan inop

Post by Mike W. » Thu Apr 25, 2019 10:35 pm

It's a pain in the ass to take apart the console at all. So start by checking for voltage and ground, which should change, at the motor wires themselves. Usually they die by wear and rattle and squeal, but I've seen them die silent deaths too and just not work.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

User avatar
maybeillbuyit
Posts: 142
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Re: Heater fan inop

Post by maybeillbuyit » Sat Apr 27, 2019 9:04 pm

Hey thx Mike, I know you’ve worked on these dials and fans a lot. I appreciate the input. Im hoping since it did seem to work a bit its maybe just corrosion on a connection or something simple. I’ll report back when I get into it.
Dave
1977 530i another project
1979 635csi Euro "project"
1987 635csi

User avatar
maybeillbuyit
Posts: 142
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Re: Heater fan inop

Post by maybeillbuyit » Mon May 13, 2019 7:01 pm

OK well I've been working on this issue today with not much success. So far I have power at the fuse that supplies the blower motor. No power at the the two wires that supply the blower motor. I disassembled the console and mostly pulled out the center console holding the center console plug as the rotary dial is called. There is power to it which I kind of knew because the clock works fine. I've also removed the fan motor assembly and tested it and the motors spins fast on just straight 12 volt from the battery. I thought at first I was looking for a heating/cooling relay but I didn't find one in there and realized I was using a BMW electrical trouble shooting manual for a 1977 630csi which apparently has a relay but my doesn't seem to :oops: I've also been using the Haynes electrical schematic for the 1977 model car and it doesn't seem correct at all. Its got more wires and different colored wires than my car has so I've given up on that. I thought there was a link to a bunch of manuals on here some where. Anyone know where that is? On the bright side I didn't find pulling the whole console apart as bad as I was expecting although maybe putting it all back won't be much fun. Pics later when I have time.
After more searching and pondering I found another separate schematic in the Haynes manual for 1977 530i's with AC which my car has, like the BMW 630sci Manual it shows a relay so maybe I do have a relay in there somewhere. Anyone have any insight where it is? I know the later cars (81 e12s) have a relay for the fan motor just below the rotary fan speed dial. I don't have one there so Im kind of stumped. Also none of my wires are the same colors as either of the schematics. Weird
1977 530i another project
1979 635csi Euro "project"
1987 635csi

User avatar
maybeillbuyit
Posts: 142
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Re: Heater fan inop

Post by maybeillbuyit » Wed May 15, 2019 10:26 am

528i-1981 wrote:
Mon Apr 22, 2019 2:39 pm
Electrical gremlins have myriad causes. The center console plug (8 pins I think, it also connects to the rear defogger switch) has a green wire with a brown stripe that brings power to the blower motor (that's the way it is on the 81 528, and I assume the same for you). I believe that the dial control with the clock changes the resistance through the ground, and that's how you get different speeds with the blower.
I just reread this and my center console plug is quite different than the later plugs. Mine only has 4 wires, black, blue, yellow and brown (ground) . It doesn't match the schematic I have at all. I can see where the red/white wire supplies power to the clock but no power seems to come to or leave the center console plug. And theres no relay anywhere. Totally confused here.
I've taken the center console plug apart and its perfectly clean with what looks like new grease in it so its not like its all gummed up like I know they can be.
More searching today. WTF have they hidden the relay :shock:

So going over Peters heater switch refurb page on the FAQs I notice that the back side of the center console where the heater control is has attached to it from left to right . Relay, therostat, and micro switch with my car has none of. I have figured out that even though my car is a MY 77 its actually a 76 model with a very different system than the later 77 and on models. Question is where is the relay etc?
Image
1977 530i another project
1979 635csi Euro "project"
1987 635csi

Post Reply