After years and years of dorment life the air conditioning system in my car has returned to life! (1500 dollars later mind you!)

HOWEVER, it doesn't always come on. Just about every time I start my car I have to replace my Number 11 fuse (the one that controls the compressor) because the old one is MELTED!

It doens't complete the connection and it wont come on.

Do I have gremlins in my system?
Should I upgrade to a HIGHER amp fuse? (its already the blue one at 25A)
Could it be a bad voltage regulator somewhere? (shot in the dark)
Do I take it back to the shop and demand my money back?
Has anyone else had this problem?

Just curious.

Richard

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1963 Ford F100 - Cummins Swap?
1985 Mercedes 300SD - 210K
1992 Ford Festiva - 92K
2001 Ninja 250 - 8K

I've read (and experience seems to bear it out) that the fuses on compressor circuits in old SD's are woefully inadequate. I know mind melted (rather than blew) several times. Replaced it with a 25 amp circuit breaker and no longer have that problem. I think my fan is a bit draggy (same circuit) so that probably contributes to the problem. Do a search and you should find a good bit of relevant info. My vote is for the proper size circuit breaker.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

What does the fuse card say you should be using?

I would never put a higher rated fuse In then what the card says. You risk starting a fire or damaging components that way.

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-Typos courtesy of my mobile phone.

Im using the 25 amp fuse now, the blue ones. Its the highest that the car takes and is what is recommended for the compressor/fan.

They did replace my 8" fan with one off an s500, its like 14". Would that draw that much MORE power?

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1963 Ford F100 - Cummins Swap?
1985 Mercedes 300SD - 210K
1992 Ford Festiva - 92K
2001 Ninja 250 - 8K

I had this same problem a few years ago and if I'm remembering correctly (by no means a guarantee ) The Auxilliary Water Pump is fed from the same fuse as the A/C Clutch. If your Aux. Water Pump is seized (as many are) or taking too much load, then it will blow the fuse when the compressor clutch tries to engage. Try disconnecting the Aux. Water Pump (there is an inline connector about 9" from the pump) and see if that solves the problem.

I'd agree with 'okyoureabeast', don't use a higher rated fuse as you risk burning out the wiring.

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown

Congrats! And just in time for Autumn, when you won't need to use it!

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'98 E300 turbodiesel

Big problem with some of the replacement 'German' fuses availible today is the fuse-body is plastic, not ceramic like the originals. With high-draw circuits like the blower or AC compressor, if there's any corrosion in the fusebox terminals, the added resistance produces enough heat to melt those aftermarket fuses without actualy blowing the fuse element. Then the melted plastic burns onto the fusebox contacts, causing added resistance. Eventually it can get bad enough to melt the fusepanel itself.
A couple years back, this started to happen with my first 240D which came with a box of 16-amp plastic fuses. Finally figured out why the ones for the blower kept melting but not blowing. Fortunately I caught it in time.

More recently, I had to repair a friends 300D where the blower fuse-terminals had melted through the plastic fusepanel. I actually had to go behind the fusepanel and transfer the circuit-wires to a set of unused terminal (fortunately there was an extra set of unused fuse contacts in the panel)
Also gave my friend a couple extra 16 amp ceramic fuses to use for the blower.
And from now on, I'm going to save my older blown ceramic fuses (at least the higher amp ones)
If I can't find ceramic replacements, at least I can pry the elements from the new plastic fuses and mount them to my ceramic fuse-bodies.

Happy Motoring, Mark

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DrDKW

Richard,

John here in West Monroe, LA. I know your pain with our wonderful heat and humidity. Here is what is wrong with your car. As your blower motor ages, it takes more amperage to run it. The fuse number 11 is for the blower motor and the blower motor is using more than 25 amps to run. It then gets hot and melts and by the way CAN BURN!!! On my 85 380se, it burned the paper fuse diagram on the fuse box lid.
Mercedes fixed this problem half way through the year 1986 by mounting an auxiliary fuse holder outside the main fuse box. It has two very stout wires with a fuse in it similar to the 80Amp fuse in your glow plug relay. Fast Lane sells this upgraded harness as do many other places and dealers. I revamped my fuse box this spring and no more overheating of the blower motor fuse.
My 86 300sdl already had this modification in it from the factory.
Basically you unscrew your fuse box and lift it up to reveal all of the wires that screw into the bottom of it. The new harness comes complete, I think it was about $40.00. and you screw the harness wires onto the lugs in the bottom of the fuse box at fuse 11. Now take fuse number 11 out and throw it away. Mount the new fuse holder outside the fuse box on the 2nd firewall. You blower motor now has a 30 amp fuse in it and you should have no problems.
Also it is true that on W126 cars up to 1986 that the aux water pump can seize and cause too much amperage at the CCU and fry the board in it. Search on here for this modification which is adding a 1 amp fuse in line to the power to the aux water pump.
I hope you get this all working correctly. DO NOT ADD A LARGER FUSE IN THE FUSEBOX IN NUMBER 11 SLOT. YOU WILL HAVE A FIRE!!!
Good Luck

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John
1986 300sdl
1985 380se

Interesting. I have a similar situation on my '83 240D. When I bought the car the blower wasn't working (although PO said he thought he recalled it working). When i checked the fuses I found the #8 fuse blown, but also the plastic of the fuse panel was melted around the terminals. I stuck in a new fuse and the blower does work, but I am wondering why the plastic melted in the first place. The #8 fuse controls the following: blower motor, AC compressor and switch-over valve idle stabilization. I replaced all the plastic fuses with ceramic ones, but I don't want to keep a fuse in #8 until I know why it was melting the plastic. So, does the 240D suffer the same problem? If so, is the fix similar? Thanks.

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
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"Back off, man. I’m a scientist” ~ Peter Venkman

Very interesting. I do not know if this was a problem with the 240D. I do know that all of our blower motors are aging and perhaps you could get an ammeter and actually check how many amps your blower motor is drawing when it is on high speed and compare that to the amperage of the fuse in number 8. I do believe that a new blower motor would probably fix the large amperage draw of an old blower motor.
My motor on my 380se appears to be fine, it blows well, but I never checked the draw on it.

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John
1986 300sdl
1985 380se

Unfortunately, I've been told that dealer-price of new W123 blower motors is up to $800 now, with the remaining aftermarket replacements up in the $400 - $500 range!

Happy Motoring, Mark

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DrDKW

True, I bought one about a year ago. The problem is that you have to buy the entire blower assembly, not just the motor. I think I paid $500 and change.

Just checked Fastlane Parts and the Behr blower for 1982 W123 with manual heat-AC is $502. With ACC it's $544.
A couple weeks ago, I priced one for an '82 300D from a local suppler at just under $400, but when his stock is gone, I guess the sky's the limit. Or some enterprising fellow may figure out how to adapt a $60 Chevy or Toyota blower into one of our cars.

Happy Motoring, Mark

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DrDKW

Yup, $544 sounds about right. These cars are finally reaching the age where the parts are going to start getting expensive. A couple of years ago I paid over $500 for one of th AC hoses on my 83 240D that happened to be a dealer only part. The newest W123s are almost 25 years old now, that will be the end of the cheap parts.

I've got a very nice almost new looking working spare blower motor. I guess I should probably hold on to it.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012