Auxiliary fan fuse gets hot and eventually fuses

Post by **Ralf_CT** » Sat 07 Jan, 2017 5:05 am

I'm experiencing a strange problem: my red 16A auxiliary fan fuse ('D') gets hot when the fan runs and eventually fuses. I've even had the plastic part holding the fuse 'wire' melting.

This seems odd as the primary load should be going through the relay, not the fuse. Any ideas?

Many thanks.

Post by **MMWA** » Sat 07 Jan, 2017 9:38 am

Do a current draw test of the fan motor(s) if excessive check for obstructions, build up of rubbish under the blades and motor (common on twin fan setup) and finally, if still excessive (probably tightening bearings) replace the fan assembly.

If this is one of the fuse box fuses, I always preference ceramic ones over the nasty plastic ones, if the fuse box plastic itself that is melting you got issues that need rectification as above. Certain environments may theoretically enable oxidisation and thus high resistance on the fuse terminals them selves causing excessive heating, but I've never seen it personally (dry as hell here in WA)

Post by **Djenka018** » Sat 07 Jan, 2017 9:57 am

Heat on the fuse itself is a sign of the poor contact.
In my experience, 99% of the hot contacts is looseness.
You may have to squash the connections on fuse socket to make a better contact with fuse blades.
Could be also the crimpin at the back of the connector.
I'd presume that the 16A is correct fuse.

"This seems odd as the primary load should be going through the relay, not the fuse"
Every load has to go through a fuse. Relays only replace the switches so that there can be a tiny switch controlling the relay which controls a big load.

Post by **Ralf_CT** » Sat 07 Jan, 2017 7:55 pm

MercMad West Australian wrote:Do a current draw test of the fan motor(s) if excessive check for obstructions, build up of rubbish under the blades and motor (common on twin fan setup) and finally, if still excessive (probably tightening bearings) replace the fan assembly.

If tight bearings, can these not simply be replaced? I suspect a new fan motor will cost a small fortune. The fan seems to turn okay, no excessive tightness.

Post by **ChristoC** » Sun 08 Jan, 2017 5:11 pm

Red (16A) is indeed correct fuse for D = Aux Fan; as far as I know the Aux Fan (hi and lo speeds) is the only device connected to fuse D in a W124.
If the fuse is blowing then it must be caused by excessive current; either shorted turn(s) in fan motor, excessive mechanical resistance, or there's some short circuit in the associated wiring.
Disconnect fan and test remaining wiring for short circuit; do that by removing fuse and measuring resistance between "cold" (i.e. the not 12V) side of fuse and chassis; If no shorts then the fan is possibly faulty.
On my W124 theres a largeish 2-pin (socket & plug) connector clipped to the chassis just behind & below the left headlight near the aircon receiver/drier - that connects direct to the Aux Fan; makes disconnecting it very easy. The fan itself measures just under 1 ohm resistance.

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Post by **Ralf_CT** » Sun 08 Jan, 2017 6:39 pm

ChristoC wrote:Red (16A) is indeed correct fuse for D = Aux Fan; as far as I know the Aux Fan (hi and lo speeds) is the only device connected to fuse D in a W124.
If the fuse is blowing then it must be caused by excessive current; either shorted turn(s) in fan motor, excessive mechanical resistance, or there's some short circuit in the associated wiring.
Disconnect fan and test remaining wiring for short circuit; do that by removing fuse and measuring resistance between "cold" (i.e. the not 12V) side of fuse and chassis; If no shorts then the fan is possibly faulty.
On my W124 theres a largeish 2-pin (socket & plug) connector clipped to the chassis just behind & below the left headlight near the aircon receiver/drier - that connects direct to the Aux Fan; makes disconnecting it very easy. The fan itself measures just under 1 ohm resistance.

Thanks, Christo, I was hoping you'd pick up on this thread. I'll follow your advise and report back.

Post by **ChristoC** » Mon 09 Jan, 2017 9:04 am

What year & model is the car?

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Post by **Christo C** » Wed 11 Jan, 2017 10:18 am

Ah yes I see "1993 W124 230E Auto, M102.982, 204,865 km, MBSA-built" in your signature when I use PC not TapaTalk on iPhone...

Here's a diagram of the cooling fan electrix on my car; as far as I can tell subsequent variants and years use a pretty similar arrangement from all the circuits I've been able to see:

If you follow the line up from Fuse D it just goes to switches in 2 relays:
- K9, which [when activated by 110deg switch in 3-pin Temp Switch S25/4] turns M4 Aux Fan on at Full Speed.
- K8, which [when activated by A/C Pressure Switch S32] turns M4 Aux Fan on at approx Half Speed [via R15 Resistor], plus Y2 Engine Fan on [via Electromagnetic Clutch].
Some variants show relay K8 as single-pole, but the function is the same for M4 Aux Fan, and Y2 Engine Fan is not switched....

Pretty simple really to observe for short circuits somewhere; I still surmise it is likely to be a failing fan, or could it be that your 1993 car suffers from the infamous "rotten wiring syndrome" I wonder.....

Post by **Ralf_CT** » Sun 15 Jan, 2017 8:25 am

Christo C wrote:Ah yes I see "1993 W124 230E Auto, M102.982, 204,865 km, MBSA-built" in your signature when I use PC not TapaTalk on iPhone...

Here's a diagram of the cooling fan electrix on my car; as far as I can tell subsequent variants and years use a pretty similar arrangement from all the circuits I've been able to see:

If you follow the line up from Fuse D it just goes to switches in 2 relays:
- K9, which [when activated by 110deg switch in 3-pin Temp Switch S25/4] turns M4 Aux Fan on at Full Speed.
- K8, which [when activated by A/C Pressure Switch S32] turns M4 Aux Fan on at approx Half Speed [via R15 Resistor], plus Y2 Engine Fan on [via Electromagnetic Clutch].
Some variants show relay K8 as single-pole, but the function is the same for M4 Aux Fan, and Y2 Engine Fan is not switched....

Pretty simple really to observe for short circuits somewhere; I still surmise it is likely to be a failing fan, or could it be that your 1993 car suffers from the infamous "rotten wiring syndrome" I wonder.....

Christo, sorry for the delayed reply, for some reason I'm not getting notifications although "Notify... " is ticked.

As suggested I checked the following:

1. 'Cold' side 'D' fuse voltage: 0V;
2. Resistance across 2-pin socket going to fan: 1.1ohms on 200 scale;
3. Haven't checked current draw with fan working (DMM not suitable);
4. Fan turns easily, no obstructions.

According to the registration docs mine is actually a 1992 model, the crumbling insulation issue was apparently only a problem with the facelift models in '94.

P.S. We've been downloading a watching some of the Australian TV series (currently on Rescue Special Ops), Sydney and surrounds looks like an awesome place!

Post by **Christo C** » Sun 15 Jan, 2017 8:48 am

Yes ammeters that read over 10A are not so common....
Only further things I can also think of
- if you unplug the fan and run engine, & possibly short the 110deg switch on Temperature Switch S25/4 (if it exists) which should turn on Aux Fan Relay K9, does the fuse still blow?
You may prefer not to try that, however, this may be a better way....
- is there is some problem with R15 Aux Fan Pre-resistor - with Ignition = Off, if you unplug the fan and measure resistance between either terminal of R15 and chassis it should ideally be "open circuit" or some very high resistance. If any appreciable low resistance is present either the resistor has an internal short to chassis, or the associated wiring to the Relays (K8 & K9) has shorts.
On my car R15 Aux Fan Pre-resistor is mounted on wing not far behind/below the right headlight next to Aircon Receiver/Dryer.
Remember to re-plug the fan.

Post by **Ralf_CT** » Sun 15 Jan, 2017 4:19 pm

On the open road I'm running at +-83 degrees, on a warm day in stop-start traffic it rises slightly above the 'unmarked' 100 mark before dropping (AC fan also comes on). I know the fuse has popped when it rises a little higher before eventually dropping, albeit slower (or the fuse has popped when the fan only comes on for 30s, or so). Are these temperatures normal? One thing I still need to do is replace the plastic thermostat housing with a cast unit.

Post by **ChristoC** » Sun 15 Jan, 2017 6:33 pm

Those temperatures are fine, but you need to find why the Aux Fan fuse blows, as without that fan your car WILL overheat in stop/start traffic - the head gasket blows VERY easily in these W124s if they overheat.

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Post by **Ralf_CT** » Fri 20 Jan, 2017 11:29 pm

Christo C wrote:Yes ammeters that read over 10A are not so common....
Only further things I can also think of
- if you unplug the fan and run engine, & possibly short the 110deg switch on Temperature Switch S25/4 (if it exists) which should turn on Aux Fan Relay K9, does the fuse still blow?
You may prefer not to try that, however, this may be a better way....
- is there is some problem with R15 Aux Fan Pre-resistor - with Ignition = Off, if you unplug the fan and measure resistance between either terminal of R15 and chassis it should ideally be "open circuit" or some very high resistance. If any appreciable low resistance is present either the resistor has an internal short to chassis, or the associated wiring to the Relays (K8 & K9) has shorts.
On my car R15 Aux Fan Pre-resistor is mounted on wing not far behind/below the right headlight next to Aircon Receiver/Dryer.
Remember to re-plug the fan.

Hi Christo, we tried shorting the 110deg switch on one of my other posts... nothing happens. Shorting the 100 deg side activates the electromagnetic fan.

I disconnected the connector near the receiver/drier earlier and connected a set of jumper cables directly between the battery and two terminals going to the motor. Lots of sparks when connecting the clamps, one could almost think there's a direct short. After running the fan for 2-3 minutes the bolt in the center of the fan got extremely hot. There must be an internal issue with the fan motor. How difficult is it to remove? Can they be overhauled, i.e. brushes replaced, commutator cut, armature rewound (if necessary), or is it cheaper just to replace the unit?

Post by **Christo C** » Sat 21 Jan, 2017 9:11 am

Ralf_CT wrote:I disconnected the connector near the receiver/drier earlier and connected a set of jumper cables directly between the battery and two terminals going to the motor. Lots of sparks when connecting the clamps, one could almost think there's a direct short. After running the fan for 2-3 minutes the bolt in the center of the fan got extremely hot. There must be an internal issue with the fan motor. How difficult is it to remove? Can they be overhauled, i.e. brushes replaced, commutator cut, armature rewound (if necessary), or is it cheaper just to replace the unit?

Yikes! That has to be your problem, and explains the fuses blowing! Unfortunately I have no idea whether the fan is repairable or has any user-serviceable components at all ....... probably cheaper and easier to replace with used or aftermarket unit....

Post by **Ralf_CT** » Mon 23 Jan, 2017 7:39 pm

Christo C wrote:
Ralf_CT wrote:I disconnected the connector near the receiver/drier earlier and connected a set of jumper cables directly between the battery and two terminals going to the motor. Lots of sparks when connecting the clamps, one could almost think there's a direct short. After running the fan for 2-3 minutes the bolt in the center of the fan got extremely hot. There must be an internal issue with the fan motor. How difficult is it to remove? Can they be overhauled, i.e. brushes replaced, commutator cut, armature rewound (if necessary), or is it cheaper just to replace the unit?
Yikes! That has to be your problem, and explains the fuses blowing! Unfortunately I have no idea whether the fan is repairable or has any user-serviceable components at all ....... probably cheaper and easier to replace with used or aftermarket unit....

The local MB agent quoted R8,700 (AUD845)! I've watched a few vids on YouTube, apparently carbon dust is the primary culprit, it collects over time and being conductive creates symptoms of a short circuit. A good clean, checking/replacing the bearings and brushes should sort it out, after all, it's only a simple DC motor. Something's wrong when the price of the part equals almost 20% of the car's value.

Post by **ChristoC** » Mon 23 Jan, 2017 8:03 pm

Great! Fascinated to learn how you get on - I'm enthusiastically with you there; I always attempt to repair anything before replacing it; just that I've never dismantled one of these fans yet.

1986 230E Saloon W124.023 M102982 = Janis
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Post by **compress ignite** » Mon 03 Jul, 2017 10:42 am

@300E&year=1992&cid=16www.autohausaz.com/search/product.aspx?sid=hlsl0fudhoov52io0rhaxubf&makeid=800016@Mercedes&modelid=1193925@Cooling%20System&gid=16732@Auxiliary%20Cooling%20Fan%20Assembly

See if These guys will ship

$66.59 USD = 88.63 AU

(I've NO Idea of shipping costs [May make it intolerable] )

Post by **Ralf_CT** » Mon 03 Jul, 2017 5:16 pm

compress ignite wrote:@300E&year=1992&cid=16www.autohausaz.com/search/product.aspx?sid=hlsl0fudhoov52io0rhaxubf&makeid=800016@Mercedes&modelid=1193925@Cooling%20System&gid=16732@Auxiliary%20Cooling%20Fan%20Assembly

See if These guys will ship

$66.59 USD = 88.63 AU

(I've NO Idea of shipping costs [May make it intolerable] )

Will the 300E fan fit the 230E? They never imported anything smaller than the 300E into the US... too slow for them. :)

Post by **compress ignite** » Tue 04 Jul, 2017 1:33 pm

I stand corrected!
The M102.XXX engine Stuttgart shipped to the US in 1992 was in the 190 chassis(They now call it a C class)
This single 15" fan is what they list for the US 190:
http://www.autohausaz.com/search/produc ... 20Assembly

Also it's a reasonably known brand name Vemo or Meyle
(and you'll note not as quite a bargain as the Uro brand which was on the 12 ")

The E class in 1992 shipped to the US has a Mechanically belt driven fan "Pulling" from behind the Radiator
with Auxiliary Electric Fan(s) in front of the condenser/radiator system.
That Link I sent was for one of the Electric "Pusher"fans which would be mounted in front of condenser/radiator.

Is there any convenient way you can shoot me a Part Number?

Post by **Ralf_CT** » Tue 04 Jul, 2017 5:22 pm

compress ignite wrote:
Is there any convenient way you can shoot me a Part Number?

Apparently A0005007193, according to Google. It's a single fan in front of the A/C condenser, pushing through both radiators. Here's an eBay link showing the entire fan/shroud assembly: http://www.ebay.com.au/itm/Mercedes-Ben ... 2521131835

Post by **compress ignite** » Wed 05 Jul, 2017 7:54 am

Apparently MB (According to "Rock Auto" an Internet parts supplier based in the state of Michigan [US])
Used that part number (000 500 70 93) in the 1992 190E 2.3L inline 4Cyl as the Auxiliary Fan setup.
http://www.rockauto.com/en/catalog/merc ... embly,2181
(BUT, RA is "Out of Stock" on that item)

The other supplier Autohaus AZ routes that part number to the also on backorder Meyle 15 inch fan.
http://www.autohausaz.com/search/produc ... ote][quote][/quote][/quote]

BUT when I look up the fan by 1992 190e 2.3L it shows not only the "Out of Stock" fan BUT th two(2) other
fan options we saw before.
http://www.autohausaz.com/search/produc ... 20Assembly

So, the 2.3 inline 4 got a 15" single auxiliary fan setup whether assembled in Duetschland or SA.

All you need is the Fan Motor...
I've "Seen" instructions and you tube videos on how to DIY W123 electric fan motors.
(BUT No personal knowledge of the newer fan motors or whether they're "User Serviceable")
Since per your description your fan motor is "Toast"...
I'd sure be tempted (If T'were mine) to [depending upon my skill level]either tear into it myself
or turn it over to a local electrical rebuilder shop.

Look at the picture of the ACM fan from this supplier (Even though it's for a US 2.6L "Six" )
http://www.partsgeek.com/catalog/1992/m ... embly.html
[I'm pretty sure it's also a 15" fan setup]
BUT (Here's why I want you to look) the rear view of the setup shows how the fan motor would be
removable from the assembly.

Post by **Ralf_CT** » Wed 05 Jul, 2017 11:13 pm

compress ignite wrote:
All you need is the Fan Motor...
I've "Seen" instructions and you tube videos on how to DIY W123 electric fan motors.
(BUT No personal knowledge of the newer fan motors or whether they're "User Serviceable")
Since per your description your fan motor is "Toast"...
I'd sure be tempted (If T'were mine) to [depending upon my skill level]either tear into it myself
or turn it over to a local electrical rebuilder shop.

I was considering getting a good used one, rebuilding it, fitting it and then rebuilding and selling my one, possibly at a price which will balance the purchase of the used one. Mine still works fine, it just gets a little hot and melts the fuse after a few runs. Now that it's winter it stays off most of the time.

While I have the knowledge to strip the unit, I lack the tools or work space. I'm sure a competent electrical shop can tear it down, clean/cut the armature, replace the bearings/bushes, renew the brushes and re-assemble.

Post by **Tony From West Oz** » Thu 06 Jul, 2017 12:05 am

I'm sure a competent electrical shop can tear it down, clean/cut the armature, replace the bearings/bushes, renew the brushes and re-assemble.

The Competent electrical shop will charge a starting price of $100 then an additional $80 per hour.
If you cannot do the job yourself, then just buy an new one that will fit, even if you need to splice the Mercedes connector onto the cable.

Post by **Ralf_CT** » Thu 06 Jul, 2017 12:41 am

Tony From West Oz wrote:
I'm sure a competent electrical shop can tear it down, clean/cut the armature, replace the bearings/bushes, renew the brushes and re-assemble.
The Competent electrical shop will charge a starting price of $100 then an additional $80 per hour.
If you cannot do the job yourself, then just buy an new one that will fit, even if you need to splice the Mercedes connector onto the cable.

Not that expensive in SA? :) I'll do as much as I can myself ... I don't like throwing repairable items away.

Post by **compress ignite** » Mon 17 Jul, 2017 11:43 am

As "Frugal" (Cheap) as I like to think myself...

I can't argue with Tony from West Oz.

Labor rates are what they are... (Where they Are)