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  #1  
Old 09-21-2009, 08:21 PM
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Join Date: Jun 2008
Location: Space Coast
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Blower motor W123

My blower motor starts strong when I turn on the A/C, but within 15 seconds starts slowing down and comes to a stop, without any screeching or anything like that. I took the motor out and tapped a bunch of gunk off it, then sprayed it with some WD40, although I couldn't good access to any frictional surfaces.

This worked for a couple of days, but now it is back to stalling after 15 seconds.

When I take the motor out and hold it in my hand, I can get it to start back up by holding it upside down. I thought first that I had bad brushes, but now I think that it might be bearings.

On ebay there is a blower amp for sale. Could my amp be overheating in 15 seconds?

I'm at a loss here, can anyone please offer some advice?

Thanks.

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1983 300TD, running on wvo because I can't stand OPEC.
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  #2  
Old 09-21-2009, 08:33 PM
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Location: Sonoma Wine Country
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Does the blower run OK if you press the "Hi speed" fan button? Problems with dry bushings usually show up at the lower speeds rather than at high speed.

Try connecting the blower motor directly to 12 volts. If it runs OK and doesn't stall , the problem is not in the motor. Personally, I suspect dry bushings or worn brushes that make poor contact as the motor warms up.

I don't know what you found on eBay but the 123 doesn't have a blower amp as such. It has an electronic module with transistors and relays; problems with this unit are usually burned relay contacts rather than overheating transistors. A burned relay contact would mean the blower wouldn't work at all on some speeds.

I wouldn't replace anything electronic until I was absolutely sure the motor was OK.

Jeremy
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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #3  
Old 09-21-2009, 08:43 PM
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Everything I described was with the fan on high speed. Thanks for the info on the lack of an amp and the electronics.
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  #4  
Old 09-21-2009, 11:47 PM
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The Push-button Unit (PBU) does the switching to control the climate control system but the blower speed is controlled by the module I described earlier. The small amount of intelligence in the climate control system changes the blower speed based on temperatures measured by various sensors in the car. The blower module lives under the dash on the climate control box.

The blower speed module also uses a set of resistors that live in a perforated metal box on the right inside fender in the engine compartment. The resistors look like coils of wire. It is rare for the resistors to fail. The resistors limit the current that the blower motor gets, thus changing its speed. The high speed blower pushbutton forces maximum voltage to the blower motor, the low speed gives minimum voltage, and the middle "auto" pushbutton allows the electronics to select the blower speed.

If the blower runs at other speeds but also stalls after awhile, I would say the problem is the blower motor, not the blower controller. If the blower runs at high speed but not at lower speeds including with the "low" pushbutton, then it could be either the electronics or the bushings in the blower motor.
__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #5  
Old 10-03-2009, 09:47 PM
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Join Date: May 2009
Posts: 16
Blower

I bought an 87 300D and the guy already bought a new blower motor. I took everything apart because of a fire or something happened around/under the blower area. i still cant find what the fire was, it smelled electrical (any hints would be helpful) but while I have it apart I was going to install this new fan motor but it doesnt have the squirrel cages on it. How do I remove them from the old one and put them on the new one?

Last edited by tisdale36; 10-04-2009 at 01:58 AM.
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  #6  
Old 10-05-2009, 02:21 AM
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I figured it out, thanks

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