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  #1  
Old 02-22-2011, 06:07 PM
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Strong Burning Smell - Heater Fan Dead

Here's the long story: The other day, I was on my way to work, and I accidentally closed all of the vents while I had the heater fan cranked to high with full heat. Once I realized what I had done, I opened the vents, only to find that the heater fan did not work. I checked the fuse (blue), and it had not blown. I messed with the climate controls, clicked the A/C compressor on and off a few times, and suddenly, the heater fan began working again.

This morning, I was thawing out my car, with the heater fan on high with full heat, when after about 4 minutes, I noticed a strong burning smell coming from the vents (not from under the dash from what I could tell). I immediately turned the fan off and investigated the source of the smell. When I couldn't find anything, I tried the heater fan again, and it would not turn on. The fuse still had not blown. I then put a fire extinguisher on the passener floorboard and drove to work.

Did I burn out my fan motor? How hard is this to replace? Why didn't the fuse blow? I'm confused. . .and cold. . .and tomorrow my poor car will be covered in a sheet of ice that it won't be able to thaw. . .

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  #2  
Old 02-22-2011, 07:29 PM
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If you are going to tell tales like this....
I think you need to update your location..
I really am not buying sheets of ice in Sacramento California...(?)..
Until you take it apart you really can not tell what burned...or why the fuse did not blow...
Some cars are easy to get to the fan... I have not tried it yet...but someone will answer soon with good info...
so just consider this a ' bump'...

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  #3  
Old 02-23-2011, 01:24 AM
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Well. . .It got down to the low 30s, which is cold for us. . .
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  #4  
Old 02-23-2011, 08:16 AM
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I do not think you can overheat the motor by closing all the vents. If it was indeed the blower motor that went, it was probably ready to go anyway.

I replaced several blower motors in my old Volvo but never had to change one in the Benz. The Volvo problem was recurring and had to do with a problem of moisture getting into the motor housing and causing corrosion. If you can get to the blower, try turning the fan by hand to see if it offers resistance. It could be that it ran out of lubrication or has some corrosion, if that is indeed the problem.
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  #5  
Old 02-23-2011, 10:09 AM
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I helped a local forum member diagnose his intermittent blower. The blower draws 16 amps on high. That's a lot of current! All elec connections must be good and solid in order for the blower to work properly. His problem was a poor fuse connection (fuse 8 from memory) and it got so hot the plastic surrounding it melted and receeded such that there was very little spring tension on the fuse and only making intermittent contact. Clean the fuse and the holder as a start, and see if that helps.
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  #6  
Old 02-23-2011, 11:04 AM
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A W123 blower fan is easy to get to. Drop the passenger side knee bolster and it's right there. It comes out by removing three screws and unplugging the harness, IIRC

A smell could be a number of things. Did it smell like ozone or burning plastic, or perhaps organic matter? Or was it sweet-smelling?

Usually a motor gets tired because the commutator brushes wear down. When they were down far enough, the motor begins to operate intermittently.

If a mouse nested in the heater box somehow, it could impede the turning of the motor and cause it to burn out.

One other possibility that would apply to the '82 300D (not sure about the 240): look to see if you have an auxiliary water pump mounted in the passenger side fender well. If that is seizing it could cause your climate control unit to overheat and even start a cabin fire. Again, I'm not sure if the 240 has one, but it's worth mentioning if you're getting a burning smell.

Read this thread: I lost it all....electrical fire high up in the dash
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  #7  
Old 02-23-2011, 11:11 AM
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Thanks for the responses. It was definitely a burning smell that more or less smelled like burning plastic. I already checked the fuse, and it is securely in place.
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  #8  
Old 02-23-2011, 11:44 AM
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Also, I have the 3 knob climate control system, not the push buttons.
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  #9  
Old 02-23-2011, 11:46 AM
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Quote:
Originally Posted by mjquillici View Post
Also, I have the 3 knob climate control system, not the push buttons.
That's good -- you're better off.
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  #10  
Old 02-23-2011, 12:20 PM
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Quote:
Originally Posted by mjquillici View Post
Thanks for the responses. It was definitely a burning smell that more or less smelled like burning plastic. I already checked the fuse, and it is securely in place.
Funola is right regarding that fuse. Make sure the connection is clean. Heat in that area will damage the fuse box. And it certainly could produce a burning-plastic smell.

Perhaps the squirrel cage on the fan is rubbing against something when it's turned up high. Probably the logical thing to do is inspect the blower motor assembly (and the inside of the heater plenum) to look for wear or obstruction. It's easy enough to get to.

Also, You may want to check the fan switch for signs of heat damage. I can't say I've heard of any failures there, but it's one more point in the circuit where current is transferred between contacts, and a corroded connection could produce heat.
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  #11  
Old 02-23-2011, 07:41 PM
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Since you are in Sacramento, there is a PNP over on Sunrise blvd/rd. Pull a blower off another 123. $26 plus a $1 core chg and tax.

some have 3 8mm screws plus one phillips screw. and some have all phillips screws. once the knee panel is dropped, takes about 3 min to remove it.

If you have a 14 volt battery for a cordless drill, use it with a jumper wire to check the blower before removing it from the car. cut off the blower plug with enough wire left on it, strip the ends and then touch it with your jumper wire.

You can remove the blower from your 240 and check it out of the car to see how it works, or to see if the squirl cage spins freely or binds up. My 80 240 was bound up when we got it last year. i just replaced it with one from the JY.
I agree there is no way you are going to burn up the blower with the vents closed.

Start with the fuse first. as was mentioned.

Charlie
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  #12  
Old 02-28-2011, 10:20 PM
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I just pulled the fan, and it spins freely. I checked the voltage at the connector, and I get 12+ V at the red wire, and 0V at the other. If I want to test the fan to see if it works, can I run a jumper from the positive terminal to one of the terminals on the fan motor? To which one do I run it? Is one a ground? Thanks!
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  #13  
Old 02-28-2011, 11:58 PM
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Quote:
Originally Posted by mjquillici View Post
I just pulled the fan, and it spins freely. I checked the voltage at the connector, and I get 12+ V at the red wire, and 0V at the other. If I want to test the fan to see if it works, can I run a jumper from the positive terminal to one of the terminals on the fan motor? To which one do I run it? Is one a ground? Thanks!
You can do that. Look at the harness for a brown wire. The corresponding terminal on the motor should be grounded, with 12 volts to the other terminal. It should run either way, but correct polarity will duplicate normal operating conditions.

If it doesn't run, give it a tap around the brushes. If they're worn down that might cause them to make contact.
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  #14  
Old 03-01-2011, 01:02 AM
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No go. How does this thing come apart? I took out the two small screws, which opens the electrical connector. I also pulled out the two larger screws, but that didn't seem to make a difference. I'm pretty sure it burned up, and I want to check it out.

Regardless, it looks like I'm headed to the PNP this weekend.
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  #15  
Old 03-01-2011, 01:40 AM
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Usually the brushes are worn out. If you took all the screws out of the plastic end cap where the wires connected and it still won't come off, Try some gentle persuasion. Was there a spring clip retaining the electrical connector to the end cap? Sounds like there was a screw holding it in place.

You may have a Siemens motor, a little unusual. If the motor housing looks like a solid can and you can't see the motor's commutator, that's probably the case.

The more standard motor is the Bosch version, which is pretty easy to overhaul. The brushes are easily accessible on that model. On the Siemens they're hidden under the squirrel cage.

If you have a vise and a drift you can drive the armature shaft out of the squirrel cage. But first, get the end cap off the other end of the motor to see what you're dealing with.

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