Heater Blower not working on any speed

[Boris3]

My heater/fan blower motor stopped working after a race weekend with too much time spent on rumbles and gators. My guess is I knocked something loose or broke something, the resistor or something else. I've got nothing on speeds 1-4, but with ignition on I'm getting power (12v+) to the blower switch (GN/BR wire). Started with the switch since I'll have to pull the strut bar and fire system hosing on top of everything else to get to the blower and was hoping for an easier fix.

Car is a 1990 325i. I've got the Electronic Troubleshooting Manual and have been following the System Diagnosis tests. YL to ground reads 0 as it should. What has me a bit confused is that I'm getting some voltage (around 5 volts) when I test the connections from the hot GN/BR wire to the other wires (YL, BK, GN, BU) at the blower switch connector where I should be getting 12. When the ETM talks about "voltage not present" does this mean 0 or just less than 12v? If the blower resistor was done should I be getting any voltage reading at all? Just want to know if there's something else I should be checking before I pull things to get to the resistor and the blower motor.

[Das Delfin]

yellow to ground should not read zero. Yellow is your lowest speed. In order for the fan to turn on there has to be at least some voltage.

you would want to check fuse 20 for power

there is a safety switch that opens to prevent overheating inside the resistor. This could have gotten jolted or messed up.

as you can see by your diagram, there isn't much to the circuit. Just fuse 20 -> switch -> resistor -> motor. Any one of these could be messed up but it sounds like it's just your motor. Most likely one of the connections came undone.

but check fuse 20 first when the car is in RUN. You could also check that K7 works..

You want battery voltage. ie 12v

[Boris3]

Thanks, jolted and loose or broken resistor / safety switch on the resistor unit is my guess. Won't know until I open things up. Blower was set at low speed while waiting in grid and I left it on during the race.

Fuse 20 in run is fine. I don't have the ac or recirculated switches hooked up to their connectors so power at YL would only be with a connection to GN/BN.

With the ignition in run, and the blower speed switch disconnected from the connector, when I test with a voltmeter at the switch connector from GN/BN to each of the other wires in the connector I get only 4.25v at each wire (YL, GN, BK) and nothing at BU.

Thanks also for the K7 relay suggestion. Something to look into.

[Boris3]

Finally got a chance to get back to this. I get 11.6 volt at fuse 20 with car in RUN. Battery voltage at the battery is 12.4 with car in off.

Replacing K7 relay with a new one makes no difference. Still get nothing at any blower speed.

Pulled the firewall cover and blower motor cover. Connections to the blower motor are fine, both power and ground connections are tight. Blower spins freely by hand. I pulled the resistor and all of the springs are fine. Safety switch looks a little corroded, so possibly the issue. Put it back in for now.

Just out of curiousity I tried car in RUN, blower on 4 = nothing. With everything still on I decided to check the connections with the multimeter at the blower motor with the blue and brown wire still connected to the motor and everything live. Touch positive to blue wire connector and negative to ground and the blower motor kicks on. Surprised me! Removed the multimeter leads and the blower motor keeps running. Will run on speed 4 and speed 3 but not on 2 or 1. Dies. When I try to go back to 3 or 4. Nothing. Blower motor will not work.

Repeated the above again just to see if I could make this happen again and got exactly the same results. Runs on speed 4 and 3 and then dies on lower speeds or if I turn key to off and then turn key back to RUN. Blower motor will not run even when I go back to 4.

I was thinking replace the resister pack before the little experiment though this wouldn't explain why the blower motor wouldn't run on speed 4. Now I know that the motor obviously isn't dead.

Open to suggestions.

[Boris3]

Tried one more experiment. Tapping on the motor housing will get it to run for a bit at all speeds but I can see sparking inside the motor. So, looks like something jarred loose inside the motor itself. Replacement time.

[Boris3]

Turns out carbon brush on the power side of the blower motor was worn and sparking. I replaced the brush with one for $4.40 from the local ACE Hardware on the chance that this was the issue. Other side had enough left for a track car. Reinstalled and blower works now on all speeds.

Great thread here on brush replacement: http://www.r3vlimited.com/board/showthread.php?t=348412

[Das Delfin]

Nice! 4 bucks beats 400 bucks!

[Boris3]

As a backup in case the brush fix didn't work I also picked up a used blower motor for $60 from a 1998 Z3 at a local junk yard. Same part # as the motor in the e30, less wear, and much easier to find.

[george graves]

Woot - yea. Bump for google-foo. You can replace the brushes on the e30 HVAC blower motor fan. I think there is even a guy on ebay that makes a living refurb-ing fans. All he does usually it replace brushed and bushings.

Last I checked the part new is $250.