melting fuse box but not fuse
 

Hi I recently purchased a 83 240D which was said to be not used for a number of years. Trying to get everything operating I found the fuse box smoking when the AC was turned on and when the blower was high speed. Not low speed.
Its the correct 16 amp Red fuse called for but the fuse don't blow, the back of the fuse receptical melts. I figure the blower is drawing to many amps but why not blow the fuse and save a possible fire?

My fuse box had the paper fuse pattern burned at the blower fuse location when I bought it. I've had a blower slowly go out and melt the cheep autozone fuses. I replaced the blower motor and put in ceramic/copper fuses and all is well.

This is going to sound really tacky, but keep those Ceramic type fuses, even when they blow. The plastic ones that melt are your problem, which is why these came ceramic in the 1st place!:D You can take the metal fuse part off the plastic fuse you have and put it on the ceramic fuse that blew and you should be OK! I havent found a source for the older ceramic fuses yet except for wrecking yards.:(

It is true that the ceramic fuses are superior, and the plastic ones will cause a heavy load to melt them, but the problem is with your blower motor, and the fuse assembly itself. a blower motor is an inductive load, it will pull more amps than the crappy pressure contact face of the fuse block has can handle. MB introduced an upgrade to the blower motor circuit in the form of a fuse kit that replaced the clip. you can do it yourself with a spade fuse kit. get a 30 amp kit, and use 25 amp fuses. 16 amp is inadequate. but more than likely, you will need to replace your blower motor soon.

John are you saying I should install a seperate power wire to my blower motor and install a inline 25 amp fuse?
And I will be looking around for a new motor. I'll check Ebay, but I did look a various sights and seen some for 5 or 6 hundred dollars which is rediculious. I replace some in my Semi trucks in the past and brand new they were $40.
Thanks all for the reply:Steve the Novice

I've also found these fuses in glass cases, and those worked as well as the ceramic fuses.

The fuse naturally gets a bit warm when there is a high current, and softens the plastic. The pressure of the spring clip then slowly shortens the fuse to the point where there is not a good electrical connection. That's when things really start heating up.

Another (likely) possibility is a failing electrical connection in the box, causing a high temperature.

Matt I guess I should see if the fuse box will come out some to see around the back. Your right when the plastic of the box melts the tang is sinking futher iinto the box which causes a lose fit. As I said its strange because the fuse it self holds up and does not blow. But the inside tang is smoking into the plastic case of the fuse box untill now I cant see it easly like all those next to it. But I will look into it futher. The car was said to be sitting for 10 years and the fuel was thick and off smelling but not black. I guess Im lucky to get it running and having so much going right for it.

I haven't looked at an old MB fuse box in quite some time, but I imagine that the tangs for the fuses are riveted to the bus bars, through the plastic base. These joints can develop resistance due to corrosion. I've never tried to fix one that went bad, rather I just replaced the box (but that was on a SAAB rather than MB).

melting fuse block
 

I had the same problem with my 91 300d,i removed the fuse and wired in a spade type holder. I used a 15amp fuse,thinking that would tell me if the blower motor was drawing too much amperage. That has been over 3 months ago with the a/c on every time the car was used and it has not blown the 15amp fuse. Your blower motor may be OK just as mine was. Don

You can still buy the ceramic fuses from the on-line parts retailers.......I do collect good ones from the junk yard, but I buy new ones too, they cost almost nothing!

Blower Fan Fuse Upgrade ('Moved outside Fuse Box)
 

Mercedes moved the Blower Fuse for the very reason Novice has described
(AND to prevent any more Unauthorized Under-Hood Bar-B-Ques)
[Fuse and Holder got moved to the Driver's side shock tower]
'Credit to GSXR for this kit explanation and picture

Yes, as you can see from the kit the blower motor inductive current is too much for the spring type fuses to maintain contact. on an SD it's a simple procedure, on the D it's more difficult. you have to remove the fuse panel or reach it from inside the dash... both are difficult. but bottom line is you have to remove the wires from the current fuse position and link them together through a new fuse holder that's designed to handle 30 amps.

Yes I think its going to be a pain. I tried breifly today but ran out of time. Unbolting the fuse box I expected it to come to me but it instead went inside under the dash. I bolted it backup because I doubt there is enought wire to it to allow me to pulll it down far enought to work on easy. Plus I didn't disconnect the battery and had visions of arcing currents and burning wires.
So if I were to go to the blower or the blower switch and cut the power line that goes to the fuse box and install my own with a fuse, where would I go to find that wire? Would it come from the fuse box to the switch or is it back fed somehow with a relay?
Any way you guys have one of the most active boards I have seen. A new thread will be page two or three in just a couple of days. Thanks for all the ideas and its good to find a board with so many Mercedes Diesel Lovers, I thought I was alone..

To update on this one. I bought a spade type fuse and holder and soldered it on the rivits on the tangs where the old fuse went. Put in a 20 amp and so far has not blown.
I can feel the wires get warm but not hot. Must be time for a new blower motor.

It may be possible to replace just the brushes in your blower motor. This has been discussed here several times over the years. The blower motor used to be available separably but not now – perhaps it is no longer manufactured. I wonder if an auto electric place could rebuilt it when necessary? In my '85, the commutator was worn so much that just replacing the brushes was clearly not going to help.