Another Bad Blower Regulator? [Solved: Bad Ignition Switch]

[emerydc8]

I just installed a new Kaehler (KAE) blower motor regulator, after the one I had installed just six months ago went bad. The motor was also installed six months ago and is from the dealer. At first the low speed stopped working, so I was running in auto and high, then the auto and high stopped working -- typical symptoms of a failing regulator that most of us have seen before.

After installing this second regulator tonight, I decided to leave the blower housing open to test it. It worked fine in low, but as soon as I selected auto it stopped working. Then it wouldn't work in any position. When I briefly applied 12v directly to the motor (bypassed the regulator), it ran at a fairly high speed., so the motor seems to be working.

I measured the voltage coming out of the terminal where the regulator plugs in, behind the brake booster. Of course, voltage between black and red is always battery voltage (approx. 12.3v). Voltages between black and yellow are 1.2v in low, 4.5v in auto and 10v in high., so I think the voltage up to that point is correct. But when I check the voltage coming out of the regulator, it is .7v in low, 250mv in auto (variable) and 150mv in high (variable). I swapped out the push button control selector with a known good unit and got roughly the same voltage readings. The 30A strip fuse is fine. I took it out and held it in my hand.

If I were starting from a clean slate, I would think the blower regulator is bad. But this is the second regulator and it did work tonight for about a minute on low before I selected auto and it completely went kaput. Could something else be causing the regulators to fail, or is it likely just bad quality regulators? It's hard to believe it was bad right out of the box. I'm not sure where to go on this one, other than to try another regulator. My concern is that if the six-month-old factory motor is intermittently bad, am I zapping regulators with it? How else can I reasonably test the motor, outside of just applying 12 volts to it?

 

[Jlaa]

I just installed a new Kaehler (KAE) blower motor regulator, after the one I had installed just six months ago went bad. The motor was also installed six months ago and is from the dealer. At first the low speed stopped working, so I was running in auto and high, then the auto and high stopped working -- typical symptoms of a failing regulator that most of us have seen before.

After installing this second regulator tonight, I decided to leave the blower housing open to test it. It worked fine in low, but as soon as I selected auto it stopped working. Then it wouldn't work in any position. When I briefly applied 12v directly to the motor (bypassed the regulator), it ran at a fairly high speed., so the motor seems to be working.

I measured the voltage coming out of the terminal where the regulator plugs in, behind the brake booster. Of course, voltage between black and red is always battery voltage (approx. 12.3v). Voltages between black and yellow are 1.2v in low, 4.5v in auto and 10v in high., so I think the voltage up to that point is correct. But when I check the voltage coming out of the regulator, it is .7v in low, 250mv in auto (variable) and 150mv in high (variable). I swapped out the push button control selector with a known good unit and got roughly the same voltage readings. The 30A strip fuse is fine. I took it out and held it in my hand.

If I were starting from a clean slate, I would think the blower regulator is bad. But this is the second regulator and it did work tonight for about a minute on low before I selected auto and it completely went kaput. Could something else be causing the regulators to fail, or is it likely just bad quality regulators? It's hard to believe it was bad right out of the box. I'm not sure where to go on this one, other than to try another regulator. My concern is that if the six-month-old factory motor is intermittently bad, am I zapping regulators with it? How else can I reasonably test the motor, outside of just applying 12 volts to it?

I believe what you want to be doing is to measure current, not voltage. When motors stall, they can suck up vast amounts of current. As well, if the regulator is really a power transistor setup (not a resistor) then what it really does is regulate current flow based on input voltage.

However, putting an ammeter in series with the blower motor is very dangerous given that it is such a high current device. Maybe you could use a non contact ammeter (the clamp kind) that measures current without being in the circuit?

 

[gsxr]

Jon, it does sound like the second regulator failed. Hopefully you purchased through FCP with lifetime warranty.

An almost-new factory blower motor SHOULD be fine. As @Jlaa mentioned, you can test current draw with an inductive (clamp-type) ammeter. However, if current draw was excessive, the 30A strip fuse should blow. Double-check the strip fuse to make sure it's 30A (not larger) and that there is only one present - I've seen them doubled up.

For grins you could swap pushbutton units from another car...

 

[emerydc8]

Thanks to both of you for the suggestions. I sent the regulator back to AutohausAZ and ordered another. The strip fuse is fine and I did swap pushbutton units. FCP Euro doesn’t sell these regulators any more, so AHAZ may be one of the only options for these regulators.

@Jlaa — I do have a meter with a clamp to measure current but since the motor wasn‘t operating at all and the voltage was so low, I doubt it would have been any notable current. If I had not sent it back already, I would try your suggestion. It’s a good idea and I should have thought of that when troubleshooting. I‘ll follow up when I get the new regulator in a few days.

 

[gsxr]

FYI: My Fluke clamp meter shows ~25A on high speed, measured at the fuse, with engine running.

 

[emerydc8]

What surprises me is that the KAE regulator purports to be Made in Germany. Or, maybe it's just the box and the plastic cover on it that are made there. The mounting holes in the regulator aren't even threaded. I had to tap all three of them.

 

[J. M. van Swaay]

What surprises me is that the KAE regulator purports to be Made in Germany. Or, maybe it's just the box and the plastic cover on it that are made there. The mounting holes in the regulator aren't even threaded. I had to tap all three of them.

For what its worth, I’ve had at least 4 KAE blower regulators fail shortly after installation…

 

[gerryvz]

I have been railing against KAE products for at least a decade and a half.

 

[Jlaa]

What surprises me is that the KAE regulator purports to be Made in Germany. Or, maybe it's just the box and the plastic cover on it that are made there. The mounting holes in the regulator aren't even threaded. I had to tap all three of them.

I have been railing against KAE products for at least a decade and a half.

Are you guys able to take apart your blown regulators to see what is inside? I don't have used one handy to take apart, but if you could take one apart, I wonder if we can identify the components inside and source them from some place like Mouser....... it seems to me that the cost of these blower motor regulators is the fancy heatsink......

 

[kwontumspeed]

My guess is anything in there is encapsulated/potted together. But following as well since I lost low speed a few months ago. Push button was replaced with an NOS OE unit found on fleabay.

 

[gsxr]

Robert is correct, the important stuff is encapsulated/potted. I don't know if it's worth the effort to de-pot and replace discrete components. If anything, I'd source the OEM Bosch early (pre-facelift) regulator and swap that onto the facelift wires+heatsink, if you want the ~$150 max savings. Otherwise, shell out $300 for the OE Bosch facelift regulator.

Photo attached below shows encapsulated/potted regulator.

More photos at this link.

 

[gerryvz]

I think the idea of retrofitting a later heat sink (for later cars) onto the "OEM" early-style regulator is probably the best way to go, today, for a quality part and not having to pay factory prices, or go with a clearly inferior KAE product.

I can remember having this conversation with Robert Fenton in the 2002, 2003 time frame, and him telling me about KAE products being bad and that he wouldn't install them on customers' cars even back then (mainly talking about fuel pump relays and the like).

 

[emerydc8]

Otherwise, shell out $300 for the OE Bosch facelift regulator.

FWIW, I was at the dealer yesterday and had them check the stock of OEM regulators (air-filtered models). They said there are two left in the US and five in Germany. Had I known they were available, I definitely would have spent the extra $150 and gone with the OEM. This job isn't much fun and I can see this KAE regulator dying early and having to go back into both of my cars in the near future. I'm thinking of investing in one or two now for that eventuality.

 

[emerydc8]

Are you guys able to take apart your blown regulators to see what is inside? I don't have used one handy to take apart, but if you could take one apart, I wonder if we can identify the components inside and source them from some place like Mouser....... it seems to me that the cost of these blower motor regulators is the fancy heatsink......

It doesn't look too complicated unless I'm missing some hidden semiconductor.

 

[gsxr]

FWIW, I was at the dealer yesterday and had them check the stock of OEM regulators (air-filtered models). They said there are two left in the US and five in Germany. Had I known they were available, I definitely would have spent the extra $150 and gone with the OEM. This job isn't much fun and I can see this KAE regulator dying early and having to go back into both of my cars in the near future. I'm thinking of investing in one or two now for that eventuality.

That is low inventory. I'm curious if there were any codes in Paragon indicating "will be NLA when inventory is exhausted", or if they plan to get more of them in stock.

It is a simple transistor, just high current / high heat. I'm not sure what would be involved in repairing & re-potting. Thanks for the photos!

 

[Jlaa]

It doesn't look too complicated unless I'm missing some hidden semiconductor.

Nice Thanks! Shucks, it is too bad we cannot read any identifying markings on the transistor.

 

[emerydc8]

With the push-button control panel supplying variable voltage in the auto position and fixed in low and high, what would happen if you just bypassed the regulator all together? At the firewall terminal where the regulator plugs in, I'm getting 1.2v in low, 4.5v in auto and 10v in high. Wouldn't that power the motor by itself? Other than completely turning the motor off in auto, what else does it do? The only time I've used auto is when the regulator started failing a few months ago.

 

[gsxr]

Jon, the pushbutton unit supplies a low-current speed signal. The regulator translates this into a high-current signal that feeds the blower. You could bypass the regulator but it would be on high speed at all times (or, always off) with no way to control the on/off.

 

[Jlaa]

FWIW I think this is a Bosch Semiconductor 30057 Power MOSFET, which seems to be obsolete and has lots of knockoffs ..... But weirdly I cannot find a datasheet for the power MOSFET. Two pics from gsxr's website.

 

[emerydc8]

Thanks guys. This is getting to be ridiculous. I just installed the new KAE regulator I received today from AHAZ and it's not working. Just to be sure it's not something else, can someone verify the reasonableness of the voltages coming out of the three-pronged terminal behind the brake booster? I'm getting 12v between black (left post facing rear) and red (center post) in all three positions. When I check the voltage between the red and yellow (right post facing rear), in low I'm getting 10.8v, in auto 7.2v and in high 4.5v. I even swapped out push-button units in case that was causing the problem.

When I plug the regulator in and check voltages coming out of the red and black wires of the regulator (where it plugs into the motor), I'm getting 1.15v in low, 1.06 in auto and 1.03 in high. You can see from the pics below. Unless the voltage coming out of the firewall terminal is wrong, it looks like they sent me another bad regulator. Is KAE really that pathetic that they can send out this many defective units? Maybe they're re-boxing URO parts.

 

[gsxr]

Jon, I forget the proper test procedure offhand, but I'm not sure if you can test without a load present (i.e., with the motor not connected, as shown in your photos). I assume the motor does not run at all, zero movement?

At the 3-pole connector behind the brake booster there should always be +12v between black and red, those are the high-current leads. The yellow should have variable voltage depending on the speed selected, this is the signal to the regulator.

Check signal voltage from the large black wire (VOM negative lead) to small yellow wire (VOM positive lead) and this may reverse your readings, i.e. lower voltage at low speed, higher voltage at high speed. This generally confirms your pushbutton unit is working properly.

It kinda sounds like another dud regulator though.

 

[emerydc8]

Check signal voltage from the large black wire (VOM negative lead) to small yellow wire (VOM positive lead) and this may reverse your readings, i.e. lower voltage at low speed, higher voltage at high speed. This generally confirms your pushbutton unit is working properly.

That's correct. In my first post, I measured the voltages between the black and yellow, versus the red and yellow. The voltages were flipped. So instead of 1.2v in high, it is 1.2v in low. Instead of 10.8v in high, it's 10.8v in low. I wasn't sure which leads to measure voltages at the firewall, but I would bet that those voltages are normal.

I requested a refund and just ordered an OEM from GVZ Mercedes in Annapolis for $295.20. I've had it with Kaehler. There is no excuse for producing that many bad regulators. They should be ashamed to even call themselves a German company. They're doing a disservice to the Fatherland.

 

[geraniumtr]

emerydc8, there's a fellow on the Peach Parts MB forum who is quite good at diagnosing blower regulator problems. You should read his posts. Go to the Peach Parts MB forum and use the search function : "W124 E420 Climate Control Issue" . You don't have to be a member. Just answer the non robot question below the search box. Read the posts by Arthur Dalton. He knows his stuff on this issue.

Regards,
Peter Weissman

Moderator edit - here is the link to the thread referenced above:

w124 94 E420 Climate Control Issue - PeachParts Mercedes-Benz Forum

so I finally decided to tackle the dead blower fan issue in my 94 E420. What the problem is: 1. Blower motor will not engage in any setting on the CCU.

www.peachparts.com

 

[emerydc8]

Thanks. I'll check it out. I am a member. Hopefully the OEM regulator gets here soon and it will put an end to my regulator tribulation! I don't know what else it could possibly be but a bad regulator.

 

[gsxr]

Jon, did you remove the 30A strip fuse for inspection, not just eyeball it?

 

[geraniumtr]

Speaking of fuses, have you checked fuse #7 in the fuse box? This powers the PBU. If bad the yellow signal wire to the regulator won‘t be energized.

Regards,
Peter Weissman

 

[emerydc8]

Yep. Held the strip fuse in my hand. It's fine. Pulled the #7 fuse and examined it. It's fine. I am getting voltage from the yellow signal wire. The only other thing I can do is compare the voltages I'm getting with my other car. I'll do that now.

EDIT: Just checked the other car. Voltage between black and yellow: 1.06v in low, 4.5v in auto and 9.7v in high. That's pretty close to the problem car: 1.2v, 4.5v and 10v, respectively. Unless the voltage behind the brake booster is wrong in both cars, it must be further downstream -- either the regulator or the motor. I hope it's the regulator.

 

[Jlaa]

Thanks. I'll check it out. I am a member. Hopefully the OEM regulator gets here soon and it will put an end to my regulator tribulation! I don't know what else it could possibly be but a bad regulator.

Man, misery is having to do a job 3x because of faulty parts………

What surprises me is that the KAE regulator purports to be Made in Germany. Or, maybe it's just the box and the plastic cover on it that are made there. The mounting holes in the regulator aren't even threaded. I had to tap all three of them.

Yeah … the regulator though is some transistor plus packaging and fancy heat sink. Who knows who makes the transistor KAE uses. I would bet the transistor is not from Germany ……. German is not known for making power transistors either ……

Hope this next time is a charm.

 

[emerydc8]

After 12 days, it finally arrived! I'm almost afraid to install it since I've had so many regulators fail on me!

Is that a BEHR logo I see on a Bosch sticker?

 

[gsxr]

I think Behr makes the aluminium heat sink, and Bosch makes the regulator.

 

[gerryvz]

You bought from MB Annapolis? All good with your experience?

 

[emerydc8]

It took a bit longer because Eddie was out for a few days when I ordered. Plus, the part had to come from Germany. Nothing he could do about that. I looked for the GVZ discount in the drop down menu but didn’t see it.

 

[gerryvz]

It took a bit longer because Eddie was out for a few days when I ordered. Plus, the part had to come from Germany. Nothing he could do about that. I looked for the GVZ discount in the drop down menu but didn’t see it.

I met another one of our forum members earlier this week, who dropped by my house. He was en route to MB Annapolis to pick up an order that he had made.

The GVZ discount was only with MB Naperville in the parts.com days. Long ago, back when the discounts were high, and the NLA-age was low for our cars.

 

[emerydc8]

Long ago, back when the discounts were high, and the NLA-age was low for our cars.

The days of driving to the local dealer for W124 parts are long gone.

 

[gerryvz]

The days of driving to the local dealer for W124 parts are long gone.

Not for all of us

 

[emerydc8]

Okay, now I'm wondering if I'm losing it. Tonight, with the key on, I plugged the new MB regulator in, turned the a/c on with the fan on high, expecting to see some voltage from the red and blue regulator output wires and . . . nada! (pic). The voltage at the receptacle is still okay: 12v between black and red, 10.8v between red and yellow in low and 4.6v between red an yellow in high (the same voltages in post #20). I plugged the motor in and still nothing. Am I totally missing something here, or do I just have the worst luck when it comes to blower motor regulators?

 

[Kyiv]

At least you've determined that regulator is not the culprit (and KAE is not a total junk)

 

[emerydc8]

At least you've determined that regulator is not the culprit (and KAE is not a total junk)

If it’s not a bad regulator then what else could it be? There’s power going in but nothing coming out. I tested continuity from the regulator’s plug connector to the red and blue output leads that connect to the motor. When i check the blue lead there is no continuity between it and any of the three female pins on the plug side of the regulator. I don’t know if this is normal.

 

[Kyiv]

I don’t know if this is normal.

@Jlaa?

 

[Jlaa]

@emerydc8 - for shits and grins, are you able to supply varying voltages to the blower motor 12, 10, 8v etc.) to observe that motor speed is roughly proportional to voltage input? And, measure current draw?

Note that this would require a DC power source with significant current capability.

Just to rule out the motor….

 

[gsxr]

Jon, I believe a load is required. Does the regulator work as expected when connected to the blower motor?

I don't think you can bench-test the regulator as shown in your photos, without a full load applied.

 

[Jlaa]

Jon, I believe a load is required. Does the regulator work as expected when connected to the blower motor?

I don't think you can bench-test the regulator as shown in your photos, without a full load applied.

Yeah!

Just in general (I'm not really sure what kind of transistor is inside the blower motor regulator) transistors are devices that control current.


It is likely that the PBU is controlling voltage drop across the base-emitter, which then allows some amount of current to go from the collector through the emitter, thus running the blower. Assuming, of course, that the regulator is BJT in this super generic example.

 

[emerydc8]

The motor doesn't run when I plug it into the regulator. I don't have a variable transformer, but when I apply 12v directly to the motor it runs.

 

[Jlaa]

The motor doesn't run when I plug it into the regulator. I don't have a variable transformer, but when I apply 12v directly to the motor it runs.

Do PBU settings lo, hi, and auto all fail to make the blower motor run?

 

[Jlaa]

@emerydc8

What is the voltage drop across red and blue WITH the blower connected, for all three pbu settings (lo med auto)?

If the the voltage drop is zero for all three settings, can you check any of the upstream connections for red? For instance that junction with the dotted line box AFTER the fuse where it goes from bk/gn to red?

 

[emerydc8]

Let me go out and check.

 

[Jlaa]

When i check the blue lead there is no continuity between it and any of the three female pins on the plug side of the regulator. I don’t know if this is normal.

NOTE I AM GUESSING HERE

I think blue, which is after the blower motor, needs to eventually find a way to ground. I do not
know if there is supposed to be anything between blue and ground (like a passive resistive component of some sort) but I conjecture that if the path to ground from blue is open, then that would cause the blower not to work.

The reason I am guessing is because I do not know if blue is on the collector side or emitter
Side of the transistor. If blue is on the collector side, then the path to ground the through the transistor and then of course blue would not have continuity with any of the other pins of the regulator.

I theorize that yellow is base, blue
Is collector, and black is emitter. Red would be the 12v supply …. Then connect to the motor, then onto blue (into the collector).

In that case, the Pbu signal could be measure between yellow (base) and black (emitter). Voltage drop across yellow and black should be small for low fan setting and higher for high fan settings.

 

[Jlaa]

NOTE I AM GUESSING HERE

I think blue, which is after the blower motor, needs to eventually find a way to ground. I do not
know if there is supposed to be anything between blue and ground (like a passive resistive component of some sort) but I conjecture that if the path to ground from blue is open, then that would cause the blower not to work.

The reason I am guessing is because I do not know if blue is on the collector side or emitter
Side of the transistor. If blue is on the collector side, then the path to ground the through the transistor and then of course blue would not have continuity with any of the other pins of the regulator.

I theorize that yellow is base, blue
Is collector, and black is emitter. Red would be the 12v supply …. Then connect to the motor, then onto blue (into the collector).

In that case, the Pbu signal could be measure between yellow (base) and black (emitter). Voltage drop across yellow and black should be small for low fan setting and higher for high fan settings.

One you have verified pbu is outputting the correct signal, then focus to see if there is any voltage drop across the motor (blue and red). If there is no voltage drop, then there is no current, which means either transistor failure or connection issue for red or black. Just theory on my part.

 

[emerydc8]

There is no voltage at all between red and blue with the motor plugged in. Here's my question: How can 12v from the connector not power the motor, but when I run 12v from a battery charger the motor runs. I had an extra connector so I tapped off the black and red terminals behind the brake booster. I'm see 12v there, but when I connect it to the terminals of the motor, nothing happens.

Can there be voltage and not enough current to power the motor? I am bypassing the regulator entirely here and sending 12v from the receptacle behind the brake booster to the motor and I'm getting nothing, even though I measure 12v through those wires.

I have to run some errands so I'll have to get back to it later. It's got me puzzled. Thanks for all the help.

 

[Jlaa]

There is no voltage at all between red and blue with the motor plugged in.

Gotcha, thanks. So no current is going through the motor.

Here's my question: How can 12v from the connector not power the motor, but when I run 12v from a battery charger the motor runs. I had an extra connector so I tapped off the black and red terminals behind the brake booster. I'm see 12v there, but when I connect it to the terminals of the motor, nothing happens.

You can have 12v across the blower motor terminals but NOT have the blower motor run (no current) if something from the +12v supply cannot pass enough current. This could be a somewhat blown fuse (partially) or flaky 12v connection or something like that. You may recall that measuring voltage is measuring the POTENTIAL for WORK. You could measure 12v as the potential for work ...... but if the wires or the fuses or whatever are not up to spec, then even though the system could POTENTIALLY do a lot of work, no work can actually be done because the weakest link in the chain is too weak to pass CURRENT (which is the actual working that is happening because CURRENT is electron flow).

Can there be voltage and not enough current to power the motor?

Yes, very possible. Here is my simplified diagram of HOW I CONJECTURE that the transistor inside the blower motor regulator is hooked up. Note that I show five connections:

• Red @ the firewall (12v) --- through some fuses and wires and stuff. This is the 12v supply.
• Red to the motor (this delivers the 12v from the red @ the firewall to one terminal of the blower motor!)
• Blue to the motor (this is the other terminal of the blower motor)
• Black @ the firewall (this is the path to ground for everything, including the blower motor)

So the way this works is ----- the PBU gives the Transistor base (YELLOW) a voltage. Think of the transistor as a faucet, and YELLOW (PBU) is the turny-handle controlling the flow of electrons that go from the collector to the emitter.

If the PBU delivers to the base (yellow) a teeny tiny amount of voltage, this means that the faucet is BARELY going to allow any electrons to flow from red through the motor and then onto blue, then through the transistor, and then to black to ground. So even though 12v exists at the supply (red @ the firewall), the motor would turn very slowly or not at all.

If the PBU delivers to the base (yellow) comparatively MORE voltage, this means that the faucet is OPEN and is going to allow more electrons to flow from red through the motor and then onto the blue, then through the transistor, and then black to ground. So in this instance, the blower motor would be really blowin'.

In your case I THINK one of two things might be happening:

• Either the PBU is not giving the right signal (which is why I asked you what is the voltage drop across Yellow @ the firewall and black @ the firewall with the PBU set to low, auto, hi.
• Or, the PBU is delivering the right signal, but something about the 12v supply is not allowing enough current to pass through. This could be one of maybe two possible issues:
  • The transistor itself is blown
  • Or, something in the 12v supply, like flaky 12v connection or flaky fuse / corroded electrical connection or something like that.

I am bypassing the regulator entirely here and sending 12v from the receptacle behind the brake booster to the motor and I'm getting nothing, even though I measure 12v through those wires.

This makes me believe that something in the 12v supply, like flaky 12v connection or flaky fuse / corroded electrical connection or Ground or something like that is happening

I have to run some errands so I'll have to get back to it later. It's got me puzzled. Thanks for all the help.

Now I am really curious as to how you solve this!