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  #1  
Old 02-07-2006, 01:52 PM
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Location: Denver, CO
Posts: 604
Heating / AC blower motor

Here is the thing. I got to the blower motor tested the wires. I get 12.3 volts when I put the Control on Defrost. I get nothing anywhere else. AND when the voltage goes to the motor it does not turn on something just clicks. I am thinking that my brushes are bad and also the controller. Can anyone verify this? Thanks This is one of the best forums i have been on.

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  #2  
Old 02-07-2006, 02:50 PM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
It says 79 300SD in your nametag, so I'll guess it is this model.
If this is the AC servo unit in use up until 1980 under the hood,
(Big black plasticy looking thing on right fender above the alternator),
then it has a vaccum operated switch that only allows blowing air on defrost.

To bypass the switch and get the blower to work with all the buttons
whenever you want do this:

Two vacuum lines come out of the bottom of the servo,
probably yellow and black, and short. Find where these two line go into
the longer vacuum harness above. You need to put in a piece of vacuum
line that connects the harness Y shaped rubber for the balck to the
Y shaped rubber for the yellow. This wil leave the two short lines
to the servo disconnected and open, and basically jumper the black to
yellow. You'll need a couple vaccum connectors and a short (under 1 foot)
piece of rubber tubing to do this (any autoparts store).

This overrides the systems cold engine lock out of the blower.
Now the fan will blow when Lo or Hi are used.
I just discovered this trick last week and it worked for me.

One more thing: You probably need the brushes replaced on the blower.
Take you no more than 1 hour to remove the blower and visually inspect the
brushes. I seem to remember that bad brushes also cause blower to only run
on Defrost. But your voltage readings indicate the culprit is the cold engine
lock out of blower.
__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250
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  #3  
Old 02-07-2006, 10:12 PM
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Join Date: Jan 2006
Location: Denver, CO
Posts: 604
rhodes2010

I do have an 80 i registered this nambe before i bought the car and the girl said it was a 79 i can not figure out how to change the name with out re registering.

When i tested the blower motor the engine was cold. Does this make any difference ? The car is apart and i can see the blower motor bolts so taking it out will be real quick.

Thanks
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  #4  
Old 02-08-2006, 12:18 AM
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Join Date: Jan 2006
Location: Denver, CO
Posts: 604
I have just extracted my blower motor and then spun it a few times and now it works, But still does not work on anything other than defrost.

Any clues?
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  #5  
Old 02-08-2006, 12:28 AM
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Join Date: May 2005
Posts: 34
Quote:
Originally Posted by 79300sdtd
I have just extracted my blower motor and then spun it a few times and now it works, But still does not work on anything other than defrost.

Any clues?
When you say you spun it and it works do you mean that it works as well as normal? I've had problemswith my motor and now just have to hit it to get it to work. The reason mine only seems to work on defrost is that it isn't getting enough voltage to get it spinning ( I think)- if it runs for a while and loosens up I can sometimes get it to work on hi and lo. Not sure if this does you any good but you might want to try running it for 15-20 minutes on defrost and then see if it will work on the lower speeds. I susepct you need a new blower motor like I do.

John

'80 500SE AMG (yes, it's a real one)
'80 300SD
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  #6  
Old 02-08-2006, 12:36 AM
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Join Date: Jan 2006
Location: Denver, CO
Posts: 604
The motor is still out of it's housing. and i have to hold it while it is on. It seems at different angles the speed changes.

I have also heard that you can get replacement brushes. Where might i get these and how do i get the motor open to replace them?
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  #7  
Old 02-08-2006, 02:08 AM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
Okay. Here we go.

Two things (and plenty folks here know more than I do,
but I just pulled two of these out last weekend and am waiting for my brushes).

1. That vacuum bypass I describe above in post #2 allows the blower to
run when the engine is cold. When the engine is cold the blower is specifically
designed to NOT run in any speed but Defrost.
The complete technical description of the Cold Engine Lockout Switch is here:

http://www.imperialclub.com/Repair/Lit/Master/281/page09.htm

The complete book is here:
http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm
Good reading.

2. Remove the fan and motor from the black plastic housing to get at the
brushes. The brushes are visible inside brass square holders at the
fan motor opening at the opposite of the fan end. I ordered brush
number 54H from carbonbrush.com here:
http://www.carbonbrush.com/automotivebrush.htm
But... I have not received them nor installed them yet. But I will
tell you they are dimensionally correct. .312" x .312".
Others will guide you to the **************.com kit here:
http://www.**************.com/store/item.php?item=123/116%20Heater%20Motor%20Repair%20Kit%20w/%20Brushes

Still others can tell you that any electric motor repair shop and even Ace hardware also have brushes.
Plenty of reasons and resources - to do this.
__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250
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  #8  
Old 02-09-2006, 12:50 PM
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Join Date: May 2005
Posts: 34
Confused

I'm a bit confused here. The end of my fan motor opposite the blades is welded shut so I don't see how I could replace anything in there. Considering the original poster is suffering the exact same symptoms as me the cure might also be the same. AmI just missing something obvious in you post?

John

'80 500SE AMG (yes, it's a real one)
'80 300SD

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