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  #1  
Old 05-22-2014, 04:48 PM
double-dammit
 
Join Date: Apr 2009
Location: Atlanta burbs
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300SDL Blower inop, crazy question...

Could it be the outboard temp sensor? I found mine unplugged, and the compressor is locked up (just bought the car) I am getting zero response from the blower on any setting. I'm getting power at the fuse in the big box, but have yet to check the one by the firewall. Thanks in advance for any info…lost here

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  #2  
Old 05-22-2014, 09:54 PM
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I don't know how hard it is to get at the Blower itself but maybe that is also unplugged. Once you locate the Connector at the Blower try to jumper wire connected to a 12 Volt Voltage Source the Blower to see if it moves.
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  #3  
Old 05-23-2014, 12:39 AM
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The motor itself is under the glovebox...couple of screws and you are there. There is also a primitive looking resistor (spring within a metal box with holes) on the pass. side fender (in the engine compartment).
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  #4  
Old 05-23-2014, 12:53 AM
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Also Could be the Ignition Switch

Try twisting the key left (counter clockwise) a "hair or two" from the run position. The contacts seem to wear over time...

So start the motor and then with a blower setting of low or high, turn the key a touch to the left.
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  #5  
Old 05-23-2014, 01:05 AM
Skid Row Joe's Avatar
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Quote:
Originally Posted by Diesel911 View Post
I don't know how hard it is to get at the Blower itself but maybe that is also unplugged. Once you locate the Connector at the Blower try to jumper wire connected to a 12 Volt Voltage Source the Blower to see if it moves.
This.

You've got to isolate the motor, in order to see if it is operable. To my knowledge, the outside ambient temperature meter has nothing to do with that possibility.
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  #6  
Old 05-23-2014, 07:43 AM
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We also need the OP to clarify what year his 126 is.

1985 or older 126s have the 123-style ACC
1986 or newer 126s have the 124-style ACC

The control panels look almost the same but everything else behind the panel is completely different. The only visible difference from the front of the panel is the Auto button between the High and Low Fan buttons. On the 123-style the Auto button is a small white button, and on the 124-style it is the same size black button as the other two fan buttons.

123-style ACC uses the stepped resistor and relay box for blower speed control. The blower is under the glove box on the passenger side.

124-style ACC uses a PWM controller for continuous fan speed control. The controller and fan are located on the engine bay side of the firewall under the wiper mechanism.
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2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

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  #7  
Old 05-23-2014, 03:16 PM
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If it's an 86, 87, 90 or 91 SDL, it'll have a PWM blower motor controller by the blower motor under the glove box. None of the remove the wiper mechanism foolishness in a 124. No primitive resistor box for the blower.

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  #8  
Old 05-23-2014, 03:24 PM
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Oh wow I thought the gen II 126s were just like the 124s. Learn something every day.

I just went through the blower-wiper-ectomy on my 124. No fun.
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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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  #9  
Old 05-23-2014, 04:14 PM
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Could be the blower motor regulator (aka bed of nails) that translates the signals from the push button unit into signals for the blower motor.

Our 420SEL had this problem.

You just need to probe the connector and see if you get 0-7V when you set the blower on high/low. If you observe no change then its could be a problem in your push button unit.
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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #10  
Old 05-23-2014, 05:26 PM
double-dammit
 
Join Date: Apr 2009
Location: Atlanta burbs
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Smile

Wow, am I glad to have found this forum!!! The car is an 86 300SDL with close to 400K according to Carfax. I bought it under the impression that the working odo was accurate, but apparently it's been changed. No matter, nice orig. car esp for the miles for 2K in my opinion. I tried backing off the ignition a hair and no go, but thanks for the tip. I'm sure it'll eventually pop up, especially with the miles it has. I will look under the glove box by the blower for the controller and test it. I can't seem to find the "porcupine" anywhere, but I'll find it. I got the new compressor (salvage) today, and it was nearly 90 here in Atl today so I guess I need to get back at it. Where would I find the numbers on the head to see if it's been changed or it's the good one? Just curious, it runs great and maintains good temp with zero pressure on upper rad. hose.

Thanks again y'all, I REALLY appreciate your help!
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  #11  
Old 05-23-2014, 05:51 PM
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Welcome to the forum. You might want to go to User CP and update your profile to list your location. Some of us love to go on "Mercedes" road trips to meet folks, deliver parts, turn wrenches, drink a beverage or two, and eat good food.
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  #12  
Old 05-23-2014, 06:07 PM
JamesDean's Avatar
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Quote:
Originally Posted by beltfed72 View Post
Wow, am I glad to have found this forum!!! The car is an 86 300SDL with close to 400K according to Carfax. I bought it under the impression that the working odo was accurate, but apparently it's been changed. No matter, nice orig. car esp for the miles for 2K in my opinion. I tried backing off the ignition a hair and no go, but thanks for the tip. I'm sure it'll eventually pop up, especially with the miles it has. I will look under the glove box by the blower for the controller and test it. I can't seem to find the "porcupine" anywhere, but I'll find it. I got the new compressor (salvage) today, and it was nearly 90 here in Atl today so I guess I need to get back at it. Where would I find the numbers on the head to see if it's been changed or it's the good one? Just curious, it runs great and maintains good temp with zero pressure on upper rad. hose.

Thanks again y'all, I REALLY appreciate your help!
The blower motor regulator inside the blower motor case. If you drop the passenger side lower dash panel, you'll see the blower case. Four or five screws hold it on. Drop that and you'll find the motor and regulator.
__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #13  
Old 05-23-2014, 10:31 PM
sixto's Avatar
smoke gets in your eyes
 
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The cylinder head casting number is by the #2 injector. You should see a string of embossed numbers in the form 603 016 xx 01 where xx is the telling sequence. Following is a picture of a #22 casting -



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  #14  
Old 05-24-2014, 06:54 AM
double-dammit
 
Join Date: Apr 2009
Location: Atlanta burbs
Posts: 8
I don't know who to thank first, but you guys are great here. I apparently registered years ago and didn't come back until recently. I'm admittedly a terrible wrench, but smart enough to know to listen to people that know what they're doing. I couldn't even think about owning one of these cars if I had to pay somebody else to wrench on it. I've had a bunch of them W108/116/123/124/126/140 (gasser)210 and others I can't remember the body code for. I loved every one of them, and glad most people don't…so I can afford them. This 300SDL is one that I need to get straightened out as my new DD, which is currently a Husky 610SM that needs to go.

I got the porcupine out, it's laying on the floor still connected. I need to get another MM today, mine is MIA again. My inclination is that the control unit is bad, but that's just a guess. The radio (factory) is also curiously inop, and wonder if maybe it was flooded at some point. Thanks again y'all
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  #15  
Old 05-24-2014, 07:34 AM
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A little background on how the porcupine operates. It is actually a PWM drive which sounds scary but really is very similar to a car stereo amplifier. It switches the dc supply on and off rapidly. It can vary how much time it spends 'on' and how much time it spends 'off' and that is how it changes the amount of energy delivered to the motor.

The way it knows how much "off" and "on" time to provide is based on the reference signal from the pushbutton controller unit. This is a dc voltage that varies from 0-6 V dc. 0 V = stop, 6 V = full speed.

There are 3 wires going in from the car wiring harness, and 2 going out to the motor. Note that both sides of the motor connect to the controller. Neither motor wire has a direct connection to battery or ground.

Red going in = dc+ from main fuse
Black going in = ground to chassis
Yellow going in = reference voltage from pushbutton controller

Red/blue going out = to motor windings. Note that they arranged the quick connectors so that you cannot hook it up wrong to the motor (otherwise the motor would run backwards).

Note that the heat sink is there because the transistors get warm in operation, and it requires a constant stream of cooling air over the heat sink. If you are testing with the regulator on the floor pay heed to this or it can damage the regulator.

I would check that yellow wire first. With the system in High fan position, or Defrost, you should have about 6 V on that yellow wire. Also make sure you have 12 V dc on the red and black coming from the car side.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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