#8 and "c" fuses- what are the correct ratings?

[Marshall Welch]

I went over my fuse box today, removed all of the fuses, and cleaned the contacts. I guess I should have taken a photo showing the colors of the fuses that were there before I removed them, but I thought the diagram beneath the box cover would be enough to go on when replacing the fuses. There were one or two, maybe more, of the blue 25-Amp fuses in positions such as #10, and my impression was that they were placed there erroneously, and/or under assumption that the car is equipped with seat heaters, which it is not. So I replaced these 25-Amp fuses with 16-Amp fuses. Now I'm wondering if I did the right thing.

Attached is a copy of the diagram that's affixed beneath the fuse box cover. It looked to me like the symbol for the #8 fuse was an open circle, the symbol for 16-Amp fuse, that had a stray mark in it, so I replaced it with a 16-Amp fuse also. Now I'm wondering if the #8 fuse symbol has actually been marked solid black, meaning it should have a 25-Amp fuse instead. Does anyone know? I do have all of the service records, but lots of them are carbon copies and are kind of hard to read, so I haven't gone through them yet to see if this ever came up before.

A few months ago I also discovered that the plastic surrounding fuse "c", for the AC aux fan, lower right corner on the diagram, had melted and the fuse was blown. I don't remember the color of the fuse that was there before- I just pulled it out and discarded it. Is 16-Amp the correct rating for this fuse?

Thanks for your help!

[VLayton]

Assuming we are speaking of your 1982....

Without heated seats that car should require NO 25Amp fuses....

All letter fuses a-d should be red 16AMP

Most likely:

#1-8A
#3-8A
#5-(nothing/spare)
#7-8A
#9-8A
#11-16A
#13-8A

#2-8A
#4-8A
#6-16A
#8-16A
#10-16A
#12-8A
#14-8A

This is just my best guess from memory, just waking up and having coffee... #6 might be a 8A on your model...

I think it goes:

Triangle=5A (not used in any W123 I've seen)
Square=8A
Circle=16A
Filled Circle=25A (only used for heated seat models and 1985 US turbo models for the MOST part)

Sometimes people put 25A in their 16A climate blower slot (typically #8 or 10) to mask a blower resistance problem.

You should be able to acquire a fresh fuse ID card for your VIN from the dealer as needed/desired-the cards bear part numbers....

[VLayton]

Oops, I answered before I looked at your card pic, but it looks like I'm mostly on it, that #8 DOES NOT look like it's meant to be 25A....

[Maxbumpo]

I think you are correct, someone has filled in the empty circle for #8. The question is why? Was there a service campaign that upgraded that fuse? Did someone add an extra load to the circuit, requiring a bigger fuse?

The part number for your card is at the bottom: 123 545 06 00. You local dealer parts desk should be able to order it for you, and if that fuse was upgraded by MB in a service campaign, the new card will reflect that (will also have a different part number). Provide your VIN when ordering the card.

[Marshall Welch]

Yes, we're talking about my 1982 300D-T. Thanks for your replies! They are very helpful- I'll leave the fuses at 16-Amps for now.

I like the idea of ordering a replacement fuse diagram card- that would be a good way to see if ratings had been changed. I just signed up for EPC.net Online yesterday so it will be easy to see if the card part number has been superceded by a new part number. By the way, EPC.net Online is really worth trying out- you can sign up for one month at a time at $3.00/month, or for $20./year.

I went over service records: at 16,045 miles, June, 1984, the car was in for 15,000 mile service. This was at the MB dealer where the car was purchased new. The brake light was on- front brake pads/sensors replaced.

Service record also says:

"Put extra fuses in.
Replace AC fuses with 25 Amp." [Underlining added for emphasis]

So I guess they blackened in the circle symbol for the #8 fuse on the diagram. I suspect they also put a 25-Amp fuse in the "c" position, for the Aux fan but again, I threw out the old fuse and don't recall its color. That might explain the melted plastic surrounding that fuse position.

It's not clear to me from the records if there was a specific problem with the climate control that the customer brought to their attention, or if the dealer just did it because of a tech service bulletin or other reason. It was in June, in Houston, TX, so I guess that would increase the likelihood of strain on the A/C- it CAN get a little warm there...

[AnthroProfessor]

THis is the fuse that always pops. It is suppose to be the red one, not the blue one. I can understand why people use the blue, but one shouldn't mask problems of the blower motor.

[Maxbumpo]

So, if the blower motor circuit is popping the fuse, what is the fix? I know that in the 201 and 124 series, the fuse for the blower motor was moved outside the fuse box and upgraded to 25A strip fuse. Was there supposed to be a similar service campaign for the 123 series?

[Don350SDL]

You are doing the right thing, using the red 16A fuses. Bigger fuses are just an invitation to trouble.

Don

[Marshall Welch]

THis is the fuse that always pops. It is suppose to be the red one, not the blue one. I can understand why people use the blue, but one shouldn't mask problems of the blower motor.

Again, I appreciate everyone's comments. This has prompted me to continue going through the service records, some of which are barely legible. I'm making a time line of when parts have been replaced, for quick reference. This has been clearly worthwhile:

October, 1987,
29,026 miles
"A/C issues- test & replace blower motor"

So, about 2 1/2 years/13,000 miles after the A/C fuses were changed from 16-Amp to 25-Amp, the blower motor had to be replaced. This makes me wonder if the blower motor was starting to have problems back when the fuses were changed.

So far I haven't been able to find either the fuse box, much less the fuse diagram card, on EPCnet Online. But maybe that's an issue for another thread, or I can always just go to a dealer.

[VLayton]

I not heard of any "corrective campain" from MB, but if it keeps blowing the fuse, the appliance should be disconnected or corrected. (In this case the blower motor)

Now I have been able to nurse sick blower motors along for extensive periods without blowing proper 16A fuses, the trick I find is to never use full speed. Low or auto for the ACC-II, or position 1 or 2 for the non-auto types such as in US 240D.

[AnthroProfessor]

blower motors draw higher amps as they age. However, there is one other component that could cause the #8 fuse to pop. Under the hood of the car is a small motor in a cylinder shaped object near the fender. That might be defective. If it draws less than 4 amps, its broken. If it draws more than 8 amps, its also broken.

[Marshall Welch]

blower motors draw higher amps as they age. However, there is one other component that could cause the #8 fuse to pop. Under the hood of the car is a small motor in a cylinder shaped object near the fender. That might be defective. If it draws less than 4 amps, its broken. If it draws more than 8 amps, its also broken.

I'm not sure what the part you are referring to above is. Could you or someone clarify this? The only thing I can think of that this might be is the aux. water pump, but the fuse designation table says this is connected to fuse #14.