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Discussion Starter #21
It looks to me that you have an issue with the 12V supply line to the regulator. The supply line shouldn't drop to zero or a very low voltage when you load it up, ie try to draw heaps of current to run the blower.
My next step would be to identify where the regulator supply line originates (maybe at a fuse or junction point) and measure the voltage at that point with and without the blower. It should stay close to 12V.
You have all the symptoms of a dry solder joint, damaged wire or corroded connection (connector?) in the supply line. All of these will produce 12V on no load but fail under heavy load.
Without checking my ACC documents the signal wire from the ACC controller seems to be doing the right thing.
To test this theory, I'm going to leave the regulator out of the equation. I'll test the motor under full 12 volts out of plug. If what you're saying is the case, it should fail to run as soon as I load it. Motor runs beautifully on bench test.
 

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Further to my suggested tests on the supply line and it's connections, another test I would try in absolute desperation, would be to bypass the regulator supply line completely. That is, disconnect the 12V supply line from the regulator (pin 3 red and yellow in my referenced circuit diagram at Post #19 ) and add a new wire directly from the battery (via a fuse would be a good idea) and then try running the blower. Warning, make absolutely sure that the live 12V wire only makes contact with the pin 3 terminal. You don't want to fry any more electronics.
Best of luck.
 

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Discussion Starter #23
I built a stand to place blower motor in. I pinned the voltage meter in the back of the plugs and am now showing 10 volts. As soon as I loaded the blower motor through that plug, it went to zero. So, I'm getting ghost voltage, usually caused by a fault in an electronic board somewhere (ac controller?).

As far as a bypass. Are you saying that the hot wire can be disconnected from the regulator plug and a new one refused to the battery and the blower motor will work with regulator? It's a large 40 amp fuse presently in the box which is not blown. There is a battery terminal right under the passenger kickplate so no need to go to battery when I can travel 15" with it.
 

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So you have proven that the problem is upstream from the regulator and as a said I suspect the blower fuse connector.
Be careful but try the hot wire test exactly as you said. The regulator should work normally even though hot wired. All you will have done is bypass the supply line and all of its connections. I would disconnect the 12V wire from the regulator just as a safety measure although technically you dont really have to.
Note this is a test only so I wouldnt leave the hot wire in place too long. Just enough to measure the voltage and see if it works.
 

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Discussion Starter #25
I'm going to check all this when I get home this evening. When you say blower fuse connector, are you speaking of the fuse box or another location?
 

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Discussion Starter #27
I found the connector you mentioned this morning. I unplugged it, looked it over for anything suspicious and placed it back together. While the wires coming in and out look the same color (red with yellow stripe) as yours, the connector looks different, like it's longer. What about ground? Could that be an issue?
 

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No its not the ground.
Try neasuring the voltages at the connector and then at the fuse f33. With and without the load. You have a high resistance in the supply line somewhere.
 

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Discussion Starter #29
No its not the ground.
Try neasuring the voltages at the connector and then at the fuse f33. With and without the load. You have a high resistance in the supply line somewhere.
Does that supply line run directly from the box through the fuse connector and straight to the regulator plug or does it make another stop such as the on off switch on the dash? I can't make too much sense from wiring diagrams since I'm not an electrical engineer. Thank you much for your help so far. I'm certain I'll figure this out with your expertise.
 

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Tests for High Resistance in Blower Regulator Supply Line

The way to read the circuit diagram below is to start with what you know, ie the Blower Motor A32m1 and work backwards until you get to the battery.

Here is my analysis;
Blower Motor A32m1 has two wires going directly to the Blower Regulator A32n1. These wires are not designated and are obviously internally connected.

The connections to the Blower Regulator A32n1 are:
Next the Blower Fuse Connector X64/1 gets its power from a RDYE (Red Yellow) wire going to MR1 Pin 2 in the Right Front Fuse and Relay Module K40/7.

MR1 Pin 2 is internally connected to Fuse f33 in the Right Front Fuse and Relay Module K40/7.

Fuse f33 which is a 40A (Amber) fuse which is designated as "Automatic temperature control; Blower motor AC" in the Fuse Chart. For the Fuse Chart see;
WIS 54.15 Fuse and Relay Box - W220 Encyclopedia

Fuse f33 40A gets its power from Circuit 30 which is designated as "Battery +ve continuous" in the STAR Circuit Wiring Diagram Abbreviations Table. For the Circuit Wiring Diagram Abbreviations Table see;
Circuit Wiring - Electrical System - W220 Encyclopedia

IN SUMMARY
The Blower Regulator is connected to a constant supply of +12V via Circuit 30 in the Right Front Fuse and Relay Module K40/7.

In your case from your posted measurements, the voltage measured at A32n1 Pin 3 (RDYE (Red Yellow) on the Blower Regulator) is NOT CONSTANT but is subject to how much current is being drawn ie how much load is applied.

You have shown that with a very light load such as when the blower motor is off you measure a good 12V at A32n1 Pin 3. The conclusion from this test is that the regulator supply wire is intact and able to deliver 12V but the wire may be damaged or contain a fault.

HOWEVER under HEAVY LOAD such as when the blower motor is commanded to go flat out you measure 0V at A32n1 Pin 3. The conclusion from this test is that the regulator supply wire has a high resistance somewhere between the A32n1 Pin 3 and the battery.

The possible high resistance is most likely to occur at the weak points which are at the various junctions in this supply line. The analysis of the circuit diagram above reveals the weak points to be:
  • Pin 3 RDYE (Red Yellow) in the Blower Regulator A32n1.
  • Both in and out terminals of Blower Fuse Connector X64/1.
  • MR1 Pin 2 in the Right Front Fuse and Relay Module K40/7.
  • Both sides of Fuse f33 in the Right Front Fuse and Relay Module K40/7.
  • And wherever circuit 30 goes from the Right Front Fuse and Relay Module K40/7, but we will leave determining that until later.
TEST 1
The aim is to ascertain if there is a high resistance in the original supply line to the Blower Regulator A32n1.

The method is to bypass the Blower Regulator supply line completely and see if the blower then works when commanded from the ACC Controller.

The best way to do this is to take a reasonably heavy wire from the +12V in the foot well and connect it to Pin 3 RDYE (Red Yellow) in the Blower Regulator A32n1. It would be a good idea to use a 40A fuse in this hot wire connection just as a precaution. Now that I have analysed the circuit diagram I conclude that it is not necessary to remove the original Red Yellow wire from Pin 3 for this test. Just remove Fuse f33 in the Right Front Fuse and Relay Module K40/7.

Once the hot wire is in place and the Fuse f33 removed, switch on the ACC and command the blower to run at maximum speed.

If the Blower still does not work we have to start the diagnosis again.

If the blower now works properly you will have positively confirmed that there is a high resistance in the original supply line and the challenge is to then find exactly where it is. My guess BTW is that it is a burnt terminal under f33.

Remove the hot wire bypass and reinstall the Fuse f33.

TEST 2
The aim is to find where the high resistance is occurring in the original supply line to the Blower Regulator.

The method is to make a series of voltage measurements on the supply line starting at Pin 3 on the Blower Regulator A32n1 and working backwards towards the battery.

Test each point with the Blower Motor off and then on and record the results.

Make up a Results Table as per;
  • Test Point: Voltage with Blower OFF: Voltage with Blower ON
  • Pin 3 A32n1: ?V: ?V
  • Blower Regulator side of X64/1: ?V: ?V
  • Fuse side of X64/1: ?V: ?V
  • X64/1 side of Fuse f33: ?V: ?V
  • Circuit 30 side of Fuse f33: ?V: ?V
It may be a bit difficult to determine which side of X64/1 is which, so just measure both sides separately and record the results.
The same applies to Fuse f33.

Post the results of Test 1 before starting Test 2.

Best of luck.
 

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Discussion Starter #31
I will get on this tomorrow. But, something you say about the relay intrigues me. Because, at the beginning of this issue, when you turned on the a c, I could clearly hear a relay misfiring noise in the engine compartment above where the blower motor goes. But when I looked for a relay that controlled the blower motor, none could be found on my chart. That's why I dismissed the noise. Now, I'm even more suspicious it could be a relay issue. Is this possible?
 

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According to the circuit there is no relay involved. The power for the blower regulator and hence the blower motor comes from Circuit 30 which is a constant 12V.
 

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Discussion Starter #33
Well, you called it right

Thanks for your help. I found fuse F33 to be hopelessly melted into the fuse block. So, it's quite obvious at this point where the problem is. I'm fishing the fuse out in little pieces and noticed the melted plastic around the blade on the hot side. Fuses are supposed to blow before this kind of damage occurs. However, it obviously did not so I'm stuck improvising. My goal is to take a 10 gauge 40a fuse link and install a new line from the small positive lug located in the passenger footwell and cut the wire a couple inches back from plug and install compression connector to new line. I'm not sure I will be able to even get the blade out that's melted into the fuse block. Now I know why I've seen a couple of w220's burning on the side of the road with flames under the hood. This is scary. So unless I bypass this with a new line as I mentioned, I'd have to buy a new fuse block which I see no point in it. Pic attached:
 

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Congratulations and well done. You must be feeling pretty pleased.

"My guess BTW is that it is a burnt terminal under Fuse f33." This was a common problem in English cars equipped with Lucas electrics. I know because I used to own several Jaguars.

What happens is that you first get a small resistance due to oxidization or corrosion and this generates a small amount of heat which then accelerates the failure, eventually melting plastic and making the resistance even higher and making the problem worse. As you say it can easily cause a fire.

To try to avoid this I ALWAYS use Permatex dielectric grease (available from any auto store) to firstly lubricate a connector, but more importantly, keep the air and moisture away from the electrical connection. Dont use just any old grease as Dielectric grease is especially designed for this purpose. It is particularly good for spark plug boots. The part number is here;
http://w220.ee/WIS_15.10_Ignition_System_General

Your suggested fix is a good one. Just use high current wire and make sure it and your connectors are well insulated and cannot be damaged by passengers.

Regards
Brian
 

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Thanks, cmitch and ricebubbles - I have added a note to the Encyclopedia blower motor link in the encyclopedia, and referenced these two posts.
 

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Discussion Starter #36
I ran a new wire with an inline 40amp fuse from the lug in the passenger footwell to the power in wire of regulator plug. All is back together, pre-safe reset and a/c working as it should. Thanks #ricebubbles for all your help.
 

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I am glad it worked out on the end. I meant to say earlier that while you could easily change the blower regulator you should test your collection of regulatirs as I suspect they will all work fine. You could then off load the spares via eBay.
Brian
 

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Thanks!

Thanks for this thread. I've been chasing my tail for quite some time now trying to figure out why my '05 S430 blower motor was intermittent and then completely stopped working. After several attempts at fixing it by replacing the blower resistor module, I finally decided to chase down other possible causes. This thread led me to discover that I had a melted F33 fuse socket, nearly imperceptible upon a casual glance. The fuse seems to have soldered itself into the socket and I cannot get it out, so I'm looking at replacing the entire fuse module ($85 on AutohausAZ right now). It seems that the melted fuse block may be more common than many of the blower motor threads on the internet would lead you to believe. Anyways, thanks again for helping troubleshoot this frustrating issue. It's 90-100deg everyday where I live in California and I'm anxiously looking forward to having A/C again.
 

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I just had the melted fuse panel failure on my CL55 W215 as @cmitch. Same wiring as W220 in this regard. I really appreciate @cmitch and @ricebubbles excellent analysis. I'm thinking about how I'm going to repair with a stock wiring path. I'd appreciate any insights.

The source of the high current state in my car is a short in the blower motor; either worn down brushes or failed motor winding insulation. Most likely the brushes... The output transistors then provide as much current as they can to the downstream blower motor. Upstream from the regulator a high current state gets the wires and the fuse hot and plastic starts to melt. The fuse doesn't blow because the fuse still sees the resistance of the regulator circuit. Eventually the high current and resultant heat will either fail the regulator transistors or the plastic melting starts forming a carbon resistor on the face of the fuse blade in the cabling path to the fuse. This is why I think both @cmitch and my car had low voltage to the regulator. Melted plastic got in between the fuse spade and the fuse clips. The fuse doesn't blow because of the regulator circuit is not a short and doesn't generate more than 40Amps. My guesses are....

1) this circuit is improperly protected for short circuits after the regulator.

I question the selection of 40 amps for the fuse in this circuit. A short at the output of the regulator should blow the circuit protection wide open within a 1/2 second or less. It obviously doesn't.

2) The fuse block can not handle current at its fused capacity

Current shy of 40amps will melt the fuse block. The plastic parts are too close to high heat areas and have insufficient melting point temperatures.

Both are design flaws.

I found a fuseblock on ebay so I'm going to modify the stock wiring a bit differently than @cmitch. In the replacement fuse block, I'm going to try a 30A fuse, and a 35A fuse. If those selections are not reliable, I'm going to use the stock 40Amp fuse and add another fuse between the regulator and the blower motor starting at 15 amps. moving upward from there. I fully expect 30Amps to work reliably. That is a lot of current...

Considering the plastic melting on the HVAC circuit, I can guess that the other two circuits, (air suspension and whatever f31 is) also have more fuse than fuse box can handle. Looking at my f31, there is some corrosion on the fuse blades. I'm going to disassemble the use fuse block, clean it, and use dielectric grease with new fuses so that heat is less likely to build up and melt things next time. The heat should build up in the fuse, not on the fuse!
 

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As a general rule, melted fuses and fusebox connections are a product of resistance in the connections, not high current. Current thru resistance causes heat.

A little corrosion causes a little heat buildup. The heat causes a little more corrosion, which causes a little more resistance, which causes a little more heat, which causes a little more corrosion, which causes a little more resistance, which causes a little more heat...

Eventually, something melts.
 
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