Mercedes-Benz Forum banner

Blower not working but blower motor fine what to check next?

25K views 20 replies 10 participants last post by  hamrt 
#1 ·
Hey,
I'm new to the board and 300D ownership. I have searched this topic but need a little guidance.

My blower doesn't turn when it's installed, but if I remove it from the vehicle and apply 12volts it turns without a problem and lot's of power.
So I figure the power isn't getting there. Where do go next?
I removed the switchs from the dash but it's a sealed unit so is there anything I can check or do with it?
Also the fuse is ok.

I know this is a common problem so if there's just a thread I can be directed to that'd be great.

Thanks
 
#2 ·
Depending on the year, and which system you have, the usual culprit is the CCU itself. When removed from the car, you can see where there is a panel that pops off, three tangs in back, gently work 'em out of the holes.
Inside is a circuit board with many soldered pins, inspect those carefully for any hair line cracks surrounding the central pin.
 
#4 ·
cleaned the CCU. Didn't see any cracks. Someone has been there before because one of the tabs was broken.
I checked the 'monovalve' and there's heat either side of it.
Double checked the fuse.

Still at a lost.
 
#7 ·
Sounds like the typical fault of the resistor pack that's called it quits. Apparently an expensive fix, if you want new parts.

I hooked up my sister's 240D's fan to the rear dome light switch and a relay. It's dodgy, but it works...
 
#8 · (Edited)
Ok got my multi meter working.
There was no power to the blower so I double checked, ahem, triple checked the fuse and noticed something.
The copper tab that the fuse sits in at the firewall side was GONE! I noticed charring there before when I changed the fuse.

So I cut a piece of wire and connected it up. Just to trouble shoot and see what would happen.
Blower comes on strong and the direction controls work. I started putting back the pieces got to the third screw and the warm blast in my face was replaced with chilling disappointment as the fan died.

So the CCU changes directions and 'seems' to work...I'm not sure if it changed fan speed because I only had a minute before the fuse popped.

The Blower sounded fine. It sounded like most blowers in most cars.

So I've read on here that a blower on the way out will cause a big drain on the power and that will kill the fuse...is that it? Is it knew blower time? Can I just replace the brushes and save myself some $$ and it will fix it??
There's a few threads about people dropping 16a and 20a fuses in there but if the fuse is blowing because it's pulling to much current wouldn't I then just be bypassing an electrical safety issue?


thanks
 
#9 ·
yes you can replace just the brushes, that's what most people do.
 
#11 ·
Sure seems like it.

Could also be that the connection between the failed copper tab and the fuse, is not sufficient to transmit the electricity properly.

If I were you, I'd get a set of the following, in used but good shape:

Fuse box
Blower motor
Climate control unit

Maybe get two of each, they're not that expensive at the yards.

If you get one from a W126, it might not work. I think the W126 has extra controls. The first gen W126 uses a very similar unit (2nd gen has a completely different CCU). The one from a W107 might also not work.
 
#12 · (Edited)
What would you expect to pay at a junk yard for those parts?

Just called two big places near me. Neither has any early 80's Merc's. The one guy told me they normally sell for $50 to $100!!!!!! WHOAH! That's a lot of cheese.
 
#13 ·
I'd start with the brushes. As they go they can cause an excessive current draw, which could be the cause of your fuse box problems.
 
#14 ·
Went to a bunch of local hardware stores including one that specializes in starters/alternators etc...and no luck.

I've got a used blower lined up but it'd be good to get this one going.

There's two other stores that I'm going to try...
 
#16 ·
Went out...took your advice an drove a fair bit to a ACE hardware..no luck!
But the guy who manages the place told me he restored old BMW bikes and cars and to check out the forums...I said I did and then said that's why I was here and then he suggested a vacuum shop across the road...
Off I go.
The guy took a few steps with my Brushes in his hand into his workshop and walked right out with these.
No charge...Told him how grateful I was for helping me and went back and thanked the guy at ACE...
I'm going to try and get this one working and keep it as a spare. I've got a used one lined up.
Bonus...the copper tab at the end of the spring is almost perfect to repair the melted tab in fuse box!!!
 

Attachments

#17 ·
always nice when a plan comes together
 
#18 ·
yeah. Just finished fitting and testing it. Ran the car for 10 mins and the fuse didn't blow..but there's a slight whine, not like an electrical motor, I think it's the new brushes getting filed down.

Job done.

AWESOME SAUCE.:)

Thanks everyone.
The more I work on her the more I love her and can see the incredible build quality and care the engineers and workers took over these cars.
 
#21 ·
Helpful Autopmatic Climate Control III System Schemtic

Looks like you may have found the root of your problem, but for you and others stumbling across this thread, here is the electrical schematic for the Automatic Climate Control III (ACCIII) that is not included in the W123 service library CD's. It shows all the connections between the different components of the system. It was very helpful in helping me resolve my ACCIII issues. Unfortunately, the website I got it off of no longer seems to be on the internet.
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top