A/C fuse melts...85 300SD - PeachParts Mercedes-Benz Forum

txsrooster · #1 02-07-2006, 11:47 AM

Like the title says.. I have a 85 300sd grey market beast of a car. She starts every morning no problems. The fuse (25amp) for the a/c blower motor will melt. It won't break, but will turn off the motor once the plastic fuse can no longer support the contacts (my guess) and the motor will stop. Not a big deal now since it is cool out, but the defroster would be nice to have and be able to count on. I tried doing an external fuse 30amp in one of those plastice tubes, but it melted the tube. I am going to try and replace the fan sometime in the near future, will this solve my problem with the a/c fuse? If it is drawing to many amps why would the fuse just blow...why would it melt down? This morning I had to replace the fuse again and reached in, turned on the defroster and then rechecked the fuse..I touched not even 15 secs after turning on the blower and got a nice little burn on my thumb. Any ideas? Maybe take out the fuse and replace the car?

rhodes2010 · #2 02-07-2006, 12:24 PM

You don't say how many miles on car.
Maybe a quick check of the blower motor is in order.
A visual inspection of the brushes will tell you a lot.

The whole process should take about a half hour, 1 hour tops.
All you need is a phillips screwdriver, maybe an 8mm socket.

Brian Carlton · #3 02-07-2006, 12:53 PM

High current draw is common in that circuit. In fact, there was a bulletin about using a separate 30 amp shunt with it's own fuse. The SD has not given me trouble in this regard, however, the previous W123 did require the shunt and the 30 amp fuse. If you are having difficulty with the 30 amp fuse installed I have to think that the blower motor is drawing an excessively high current. Nothing else on the circuit would create such a draw.

Pull the motor out and see if it spins freely. I'll bet that it does not. Carefully clean it and add some lubricant to the bearings and reinstall. The current will probably drop to tolerable levels.

txsrooster · #4 02-07-2006, 03:22 PM

When I bought it, the odometer stop working at 143000, and I know I have put 50K since I owned it and that was. Plus what ever miles were put on it before the switch on its importation. So I say well over 200K and she will pass just about anything on the highway.

mercedesmatt · #5 02-08-2006, 12:03 AM

there is a outboard strip fuse modification available from mercedes for this.
I have installed several over the years and it works great. Sorry I dont have the part number at hand. seems like it is about $60.00 for everything that comes with it, stripe fuse, fuse holder, mounting bracket, wiring harness, and hardware to attach it with.

you just remove the fuse block and wire it in on the back side of the old fuse location and mount it on the left front fender well. takes about and hour to do.

the circuit wasnt designed heavy enough originally. when the blower motor starts to wear it will draw more current. thus the fuse overheats and melts sometimes melting the fuse block too, causing poor connections for the replacment fuses multipling the original problem.

my advice is leave your motor alone and add the strip fuse. I think you will be happy with the results.

H-townbenzoboy · #6 02-08-2006, 12:26 AM

Quote:

Originally Posted by mercedesmatt

my advice is leave your motor alone and add the strip fuse. I think you will be happy with the results.

I have the MB strip fuse installed, and it works, but you'll have to replace the motor eventually. I have heard as the spinning resistance becomes greater over time, it will become a fire hazard.

txsrooster · #7 02-08-2006, 08:45 AM

Any Idea where I can get one of them new fangled strip fuses at. A google search turned up nothing. Would a fuse like that be available at a autoparts store like autozone or the sorts?

mercedesmatt · #8 02-08-2006, 08:26 PM

as far as i know it is only available from mercedes, I have bought all mine from the dealership. Ive installed probably 6 or 7 of these only had to replace the motor in 1 car about a year after the fuse was installed, due to worn brushes. I believe I would try it first before i bought a $200 motor.

Brian Carlton · #9 02-08-2006, 08:34 PM

Quote:

Originally Posted by txsrooster

Any Idea where I can get one of them new fangled strip fuses at. A google search turned up nothing. Would a fuse like that be available at a autoparts store like autozone or the sorts?

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?header=header.jsp&footer=&product=1265403013&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&clientid=catalog.mercedesshop

mercedesmatt · #10 02-08-2006, 08:40 PM

thats it!! looks just like the one i get from mercedes. Wonder if theirs comes with the mounting bracket? some 126's dont need the bracket because there was one already installed on the left front fender and wasnt used.

Brian Carlton · #11 02-08-2006, 08:45 PM

Quote:

Originally Posted by mercedesmatt

thats it!! looks just like the one i get from mercedes. Wonder if theirs comes with the mounting bracket? some 126's dont need the bracket because there was one already installed on the left front fender and wasnt used.

I bought it many years ago for the W123. It had a place to screw the fuse holder to someplace on the body of the vehicle. Installing it was a PITA, I'll tell you that. But, I understand that the fuse box can be removed. If I had known that it would have been much easier than trying to snake a screwdriver up behind the dash while looking with one eye.

GeorgeT · #12 08-15-2007, 07:19 PM

The part number is 1265403013.

vstech · #13 08-15-2007, 07:29 PM

I would think a standard push in fuse holder would suffice... 10 GA *(30A) fuse holders are available for around 5.00 at any auto parts house. they even have 30 or 25 amp circuit breakers that fit in the holders so when the motor draws too much juice, it can automatically reset itself... that's what I did to my car. of course the motor eventually quit, so I did end up replacing it too...

85chedeng300D · #14 08-15-2007, 10:50 PM

Quote:

Originally Posted by Brian Carlton

I bought it many years ago for the W123. It had a place to screw the fuse holder to someplace on the body of the vehicle. Installing it was a PITA, I'll tell you that. But, I understand that the fuse box can be removed. If I had known that it would have been much easier than trying to snake a screwdriver up behind the dash while looking with one eye.

How to remove the fusebox assembly for the W123? I might have to do it in the future. I keep on replacing that blower fuse every now and then. That PreformanceProduct fuse is a good upgrade for the AC circuit.

GeorgeT · #15 08-16-2007, 12:57 AM

Here's what it looks like under that neat fuse block. I did the upgrade for the A/C fuse in the 300SD. Hopefully this will put a stop to the daily change out in Houston from running it on high, which is required right now. My only concern is that if this one blows, the link is going to be hard to get. If I have to replace it, I'll probably go with a BUSS version from Autozone, NAPA, etc since those fuses are common. The official upgrade part # doesn't resolve well in the searches. Performance products is the best place you can easily locate, but if you use part # 1265403013 and search it appears as "wiring harness" in the various internet stores.

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?header=header.jsp&footer=&product=1265403013&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&clientid=catalog.mercedesshop&cookieid=25L0XJTQA25P01Z3PB

George
300SD 1983