2000 R129 Blower Dead

[BarryFish]

Help !
My 2000 SL A/C was working fine when I parked it 2 weeks ago. Now after returning from China, (don't think the trip location matters) the blower does not run at all. I've tried every setting and it does not spin.

I checked all of the fuses for ac and they are ok.
The compressor clutch engages when there is a call for AC, just no fan.

Any idea of the common problems? (also I need a little pointing where to look physically as the car is new to me and the only thing that I've had apart is the enture trunk and latch system.) I'm good with electronics and will even troubleshoot the controller to the component level.

Any pointers to drawings / manuals would also be appriciated.

Best Regards,

Barry

[Gilly]

Barry
I'd need to grab an electrical manual and check, but here is a possiblity; the ignition switch. I believe there is a dedicated line out of the ignition switch to the fusebox, the power runs through the fuse and to the blower motor controller. These ignition switches are notorious for failing like this. The best course to check if this is true is to find the most likely fuse (should be one labelled something like ""blower" or "climate control fan". something like that, and check BOTH sides of the fuse to see if it's getting power at all. You can also try gently turning the key back and forth and see if it suddenly starts working (run it on defrost, that'll give the biggest effect so you'll know immediately if you got power to it suddenly)

Gilly

[BarryFish]

Thanks Gilly.

I'm trying to squeeze a few hours of diagnostic into the weekend. Sombody stop me if you have the answer or I'm headed down a dead-end path.

I'll check for 12V at the fuses. If it is not there I'm jumping it in.

If I've got 12V I'm going to uncover the blower motor / power control module and see if I can reverse-engineer the power and control signals. Apparently there is a control voltage (something like 0.8 to 9V) that sets the blower speed.

I figure that there can't be that many wires just to control the blower. I'm guessing 2 big ones for power and a few smaller ones like control voltage in, maybe on/off and possibly a velocity feedback.

I'll record my efforts for the benefit of others.

Regards,

Barry

[Gilly]

Barry:
"YES" on the checking the appropriate fuses, and if you find a "dead" fuse, either jump in 12V and see what happens (I did that on the one I found), and/or you can wiggle the ignition key a little and monitor the voltage, you may be able to prove the "ignition switch" theory that way- I did.
Assuming you're in good shape on that, you could also just go direct to the motor and jump in power and ground, quick easy way to test the blower itself. There are only the 2 heavy wires going to the motor itself, everything upstream of that takes care of the current supplied to the motor.

Gilly

[BarryFish]

It's Fixed ! (sort of)

I signed up for the online manual and investigated the diagnostic modes of the control unit. Blower control voltages were fine and varied with the fan speed setting.

I drove and watched the system vars and everything seemed OK.

I dug out a meter and started checking the fuse voltages with the key in pos 2 - engine not started.

About 2 seconds after the last good measurement of the 4 A/C circuits, the blower started and has not stopped yet. I do not think that it was a loose fuse as I've had them out twice and the fit and connection is good.

I think that it just knew that I was not going to give up and that I was ready to rip the motor and power control module out.

As a relentless troubleshooter, I've seen this happen with other systems too.

I now have an education on the A/C and control systems.

Thanks for the hep !

Barry

[Gilly]

Happy to hep, but a bit confused.
During the testdrive you said that it was working, seemed to indicate that anyways.
Then jump ahead to "ignition in position 2" you make it sound like maybe the blower wasn't working,

About 2 seconds after the last good measurement of the 4 A/C circuits, the blower started and has not stopped yet.

. WHEN did it stop working? Sometimes it takes at least a few seconds for the blower to spool up (due to the control unit I imagine).
I'd get it in the failed state again (HEY unless it really IS fixed, which I doubt) and go after the fuses right away.

Gilly

PS is "4 AC circuits" both sides of 2 fuses? You should be able to find the one responsible for this, maybe just by pulling them one at a time with the fan operating, there should be one that stands out as being most likely by the description on the fuse list.

[BarryFish]

Sorry for the confusion. Here's what happened in sequence:

A/C ceased working after car was garaged for 2 weeks.

Lots of driving but no blower.

Checked Fuses (twice)

Wrote to this thread, started learing about how the system works. Got online manual for n22 control. Ran diag mode:Blower control voltage stationary and driving. Control voltage OK, but no blower operation.

Tested fuse voltages w/engine stopped - key in on pos. Some loose connection must have connected or a controller fault was reset during the measurement of the voltage on each end of four fuses. (all voltages and fuses ok)

Blower starts working, not necessarily in sync with any fuse plugging or testing.

Prior to the blower starting to work, I pulled & pushed wiring harnesses near plugs and also hammered the fuse and relay boxes to look for a loose or oxidized connection.

Yes it's bad news to rely on something that just starts working, but it is hard to troubleshoot something thats working properly.

Regards,
Barry

[Markymark]

You probably just had a dead spot in blower motor. Especialy if it was sitting for a while and when you were tapping around you kicked started it. I've seen that happen alot with blower motors. I didn't read your whole post and not sure if you had already tapped on motor to get it to start or not but thats what it sound like. Just my theory.