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  #1  
Old 09-14-2020, 01:30 PM
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240d blower motor fuse keeps melting

So recently I pulled apart my blower motor since it was making noise in the bearings. While I was lubricating the bearings I decided to overhaul the motor with new brushes and lubricate everything. After I reinstalled the motor I noticed that the number 8 fuse for the blower motor and AC compressor clutch kept blowing after a few minutes. After testing the blower motor on full blast and the AC knob in the off position it still kept deforming the fuse. So I am curious as to what could be making the blower motor draw so much amperage to blow a 25amp fuse. (I installed a blue 25amp fuse instead of the red 16amp fuse because the AC clutch would draw too many amps and blow the red fuse in a minute at most) Any thoughts appreciated!

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  #2  
Old 09-14-2020, 01:58 PM
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Trying to set the car on fire? Increasing fuse size is a great way to do it.

Put the 16A back in. Find the reason for the excessive current draw. If the clutch is drawing that much power, it's junk. Replace it before it burns your car down.

Melting fuses rather than blowing fuses are usually due to overcurrent or a poor connection. The fuse boxes in these cars are notorious for poor connections with the fuses, try sanding the brass clips for the fuse with some sandpaper if it looks crusty.
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Old 09-14-2020, 02:08 PM
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On a 240D the fuse holder #5 is not used. If the contacts on #8 are burnt try swapping the wires over to #5 *after you fix the issues*.

The fuse box drops down into the inside of the dashboard. The wires are long enough to lay the fuse box on the floorboard to work on it. Of course disconnect the battery first.
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Old 09-14-2020, 03:09 PM
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@diseasel300 Thanks sorry Im going to change it back to the original red fuse I value my classic Mercedes and I do carry a car fire extinguisher in the cabin as a precautionary measure and to save a life if the time ever comes. Also I'm using those plastic fuses can anyone give me a link to the proper ceramic ones please
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Old 09-14-2020, 03:22 PM
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Quote:
Originally Posted by ASteele View Post
Also I'm using those plastic fuses can anyone give me a link to the proper ceramic ones please
There's a big part of your problem. The design of those torpedo fuses dissipates a lot of heat on the contact ends simply due to the small contact area and low spring pressure of the fuse clip. The plastic bodied fuses simply cannot support a constant high amperage draw of something like a blower motor.

Depending on where you are, some auto parts stores carry the ceramic fuses. I know Car-Quest here does. If no luck at the auto parts store, Amazon is another good source, you can get a decent quantity and keep spares in the glovebox. Only buy brass or copper element fuses, if the element looks grey or silver, move on.
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Old 09-14-2020, 05:26 PM
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@Diseasel300 Thanks I'll go get some of those and I fixed the problem by cleaning the contacts with sandpaper and loosening the bolts on the blower motor housing a little to create less friction on the bushings/bearings and installing a red 16 amp fuse. I also had to push the connector for the compressor clutch down further on the connector since the wire under the clip was a little tight so I gave the wire more slack and made sure it was installed all the way down. I assume it shook loose from vibration, but nonetheless after a 15 minute test drive with the AC on full blast the blower motor and compressor never once stopped and I checked the plastic fuse when I got back and it did not deform whatsoever so success!! I will be replacing all fuses with the ceramic ones once I get my hands on some anyways thanks for the help!
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  #7  
Old 09-14-2020, 06:09 PM
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Never overlook the crusty connection. Any time you find something getting hot, treat it as corrosion or loose! Most of the time these blower fuse issues aren't the motor itself, it's just the connection with those crappy torpedo fuses!
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  #8  
Old 09-14-2020, 10:20 PM
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Quote:
Originally Posted by ASteele View Post
@diseasel300 Thanks sorry Im going to change it back to the original red fuse I value my classic Mercedes and I do carry a car fire extinguisher in the cabin as a precautionary measure and to save a life if the time ever comes. Also I'm using those plastic fuses can anyone give me a link to the proper ceramic ones please
Regular autoparts stores sell the ceramic bodied fuses you just need to take a good look at them. At one time all Euro Cars use to use that same style of fuses.
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Old 09-14-2020, 10:24 PM
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By the Way I used to buy fuses for my US Cars at 99 cent and similar stores.
2 years ago I my Van died in traffic. I had it towed home and found the plastic body on the fuse in the run circuit to the coil had melted but the metal was still intact.
From that time I replaced the fuses with better quality ones and have had no issues.
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Last edited by Diesel911; 09-15-2020 at 12:32 PM.
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  #10  
Old 09-15-2020, 12:12 AM
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Post Ceramic Fuses

Most VW / Porsche shops / partshaus' will have the correct ceramic ones in stock cheaply .
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Old 09-15-2020, 10:53 AM
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I'm betting the blower is a dud. The bearings have probably worn out and its overdrawing. The only time I had trouble with the plastic fuses was when my blower motor did the same thing.
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  #12  
Old 09-15-2020, 12:31 PM
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Quote:
Originally Posted by dude99 View Post
I'm betting the blower is a dud. The bearings have probably worn out and its overdrawing. The only time I had trouble with the plastic fuses was when my blower motor did the same thing.
Yet if you don't have a fuse with a plastic body the body cannot melt before the metal strip does.
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  #13  
Old 09-15-2020, 12:34 PM
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Quote:
Originally Posted by Diesel911 View Post
Yet if you don't have a fuse with a plastic body the body cannot melt before the metal strip does.
Exactly this. A failing motor that's drawing excessive current will cause the element to fail, not the fuse body. Heat from a poor connection is what makes the plastic fuses melt.
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  #14  
Old 09-16-2020, 04:31 PM
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Post W123 HVAC Blowers

I agree that the bearings are usually dry and have high friction, not that they're worn out per se ~

I've taken quite a few og them apart and after taking the extra time to fully clean out all the accumulated dust and dirt then soaking the oillite bushings before re assembling with new brushes I have noticed they turn by hand *much* easier and come on sooner in the Klima II equipped cars .

If you're blowing / melting fuses and don't want to bother with the mess of fully servicing and 40 year old electric motor, just buy the $100 URO one, it fits and works .

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