Please help guys, I'm pulling my hair out!!!

Recent (past six months or so) blower motor replacement. Stopped working the other day.

No voltage at blower.

CCU has power from fuse #10

No power to or from fuse #11

Providing power to fuse #11, still no blower function.

Grounding cold engine switch, still no blower function.

My cd manual has no schematic showing me where fuse #11 derives power.

My sincere hope is that #11 takes power from the control relay

CCU has continuity through all traces and pins as best as I can test.

Blower control relay clicks as various fan speed buttons are pushed and has no obvious burned traces or cracked solder.

Anyone have a complete schematic for this or been through the same process?

Thanks guys, it's getting ready to get cold again down here!

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1998 E300 +310,000K
1996 E300 +460,000K

I don't have the diagram in front of me but I went through something similar on a 500SEL, a different fuse powered the blower that wasn't listed on the fuse chart. It had a hairline crack in it, check all your other fuses and see what you find.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Fuse 11 is powered through the ignition switch (run position only.)

So, hinky ignition switch maybe?

Does the switch also provide any power to the blower relay itself?

I jumpered power to fuse #11 and still got no blower, but the blower runs fine with 12v applied directly to it.

Thanks.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

It's difficult to troubleshoot that system without a proper test device.

The issue can be the CCU, the temperature controller, or the blower controller. When the SD lost the blower, the CCU was the culprit. But, I had to throw parts at it because of no good way to test the electronic devices.

Yeah. I was looking in at the CCU test procedure in my CD FSM and thinking that test box would come in quite handy about now!!

Oh well. Gonna rig a fused 12v circuit with a rehostat directly to the blower until I can get this sorted.

If I can find a know good used blower relay, I guess I'll start there. $200 for a relay, $200 for a CCU. Can get expensive just tossing parts at it.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

I think I would start by restoring power to fuse 11. That's the primary source of power to the ACC (push botton control and blower regulator.) The temp control unit is powered through fuse 10.

Weird, huh. My push button controller is working. If I push the various buttons the temp changes (Full defrost button to the left) and the blower relay clicks.

That's why I was going to run the blower motor manually. I'm getting heat and can adjust the temp.

Let me meter out everything again and post back.

I swear I remember metering fuse 11 while the ignition switch was in run.

More to follow...

And thanks, guys. This one's wearing me out.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

You'd figure by age 46 I'd have learned some patience.

I found the 300SD air delivery wiring schematics on my cd manual. Fuse 11 provides power to the blower only. The rest of the CCU operations are via fuse 10. That dilemma solved.

Still have no power at fuse 11 and no blower operation when providing fuse 11 with 12v.

I reckon a bad ignition switch was my problem the entire time. By tearing into stuff without sitting on it for a while and collecting the proper data, I think I toasted part of my CCU.

Yesterday evening, I had the blower relay unplugged and found 12v and a ground and jumpered them. My blower came on.

My CCU also made a nice ozone smell and emitted a puff of smoke.

So, I'm afraid I let the smoke out of the part of my CCU that sends smoke to my blower relay, thus necessitating not only an inexpensive ignition switch, but a pricey CCU as well.

Yippee!!

Have my blower on a separate switched circuit right now so I at least have heat.

Thanks for all the help, guys. I'll keep posting here as things develop.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

On a positive note, I replaced all the little 3w bulbs while I was in there. Even replaced the spider bulb so now my gear selector panel is illuminated!

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1998 E300 +310,000K
1996 E300 +460,000K

That is certainly not what the schematic in the 1982 Electrical Troubleshooting Manual indicates.

Are we dealing with a North American W126.120?

Yes.

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1998 E300 +310,000K
1996 E300 +460,000K

Here it is:

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1998 E300 +310,000K
1996 E300 +460,000K

That's interesting. That schematic is also in my book. I was looking at a fold out page-clearly labeled for the 1982 300SD-that shows that the push-button unit is powered by a red/yellow wire from fuse 11, with a different red/yellow wire powering the blower regulator, also from F11.
I find no explaination for the differences.
Take a look at pages 104-105. They also depict the two rd/yl wires from F11 to the ACC.

No affiliation, but some folks have purchased cruise amps from this seller and have had satisfactory dealings.....

http://cgi.ebay.com/ebaymotors/Mercedes-Benz-Climate-AC-Heater-Control-380-300d-126W_W0QQitemZ120209788097QQihZ002QQcategoryZ33545QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John