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Hi All Looking for some help....1976 450 SL When I start the car the blower motor stays on constantly....I pulled
the panel off so I could disconnect the switch and even when the 7 pin switch is disconnected the fan still runs??
Any suggestions would be greatly appreciated
Any
 

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1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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Hi All Looking for some help....1976 450 SL When I start the car the blower motor stays on constantly....I pulled
the panel off so I could disconnect the switch and even when the 7 pin switch is disconnected the fan still runs??
Any suggestions would be greatly appreciated
Any
Sounds like someone has bypassed it?
Does the fan speed switch work? ❔
Or maybe the 7 pin is going nuts.
Are there other wires to the blower motor?
 

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Discussion Starter #4
Sounds like someone has bypassed it?
Does the fan speed switch work? ❔
Or maybe the 7 pin is going nuts.
Are there other wires to the blower motor?
Hey Thanks for the feedback...
when I turn the fan switch there is no change in the speed of the fan
the connector on the blower is an 8 pin

Maybe the fan switch and ac switch are bad?
I will reconnect the fan switch and disconnect the ac switch and see what happens
 

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Discussion Starter #5
If your AC is on then that fan switch will be bypassed and the fan will run at a minimum speed setting.
Hey Thanks for your reply
When both switches are turned ccw all the way the fan still runs.

the bower is an 8 pin connector so it might be getting power from the ac switch????
 

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Discussion Starter #6
Hey Thanks for your reply
When both switches are turned ccw all the way the fan still runs.

the bower is an 8 pin connector so it might be getting power from the ac switch????
I disconnected both fan switch and ac switch and the blower ran when the key gets turned to power.
I get no change in speed on the fan when either switch is connected and turned.
my guess is a fault in the blower motor plug...any input is welcome thanks
 

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1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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My blower has an 8 pin connector.. My fan speed switch was faulty - worked on all speeds but demist so I replaced it $$ years ago.. I think its more likely the switch than the 8 pin. I recall somebody fixing a fan speed switch some time ago. Maybe search this forum for fan speed switch?
 

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Discussion Starter #8
My blower has an 8 pin connector.. My fan speed switch was faulty - worked on all speeds but demist so I replaced it $$ years ago.. I think its more likely the switch than the 8 pin. I recall somebody fixing a fan speed switch some time ago. Maybe search this forum for fan speed switch?
I went back 200 post and did not find it.....I disconnected the ac switch and the blower fan switch and the blower still came on when I turned the key...I will try to get a diagram of what the 8 pins control on the blower motor and try to apply power to see if I can duplicate what a good switch would do....Do you know of a good schematic or repair manual? thanks for your input!
 

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1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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I went back 200 post and did not find it.....I disconnected the ac switch and the blower fan switch and the blower still came on when I turned the key...I will try to get a diagram of what the 8 pins control on the blower motor and try to apply power to see if I can duplicate what a good switch would do....Do you know of a good schematic or repair manual? thanks for your input!
There is an ETM manual with all sorts of info. Its part of the larger manual. Look in the Encyclopedia Germanica section up top in the forum and you'll see a reference with a link..
 

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1976 450SL 156K miles
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I went back 200 post and did not find it.....I disconnected the ac switch and the blower fan switch and the blower still came on when I turned the key...I will try to get a diagram of what the 8 pins control on the blower motor and try to apply power to see if I can duplicate what a good switch would do....Do you know of a good schematic or repair manual? thanks for your input!
There is a secondary power feed to the blower; on the engine side of the firewall (passenger side) there is a multi-pin connector; if you disable one of pins (I think 8 but don’t quote me) it will turn off the fan and allow it to run according to the dash switch selection. My fan (1976 450SL) was doing the same thing and I found some random video on the Internet where some guy demo’d the work-around.
 

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1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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Search Heater Blower unit tutorial by GluekAuf in 2010. It's in the Sticky section in climate control (well down)i
 

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Discussion Starter #12
There is a secondary power feed to the blower; on the engine side of the firewall (passenger side) there is a multi-pin connector; if you disable one of pins (I think 8 but don’t quote me) it will turn off the fan and allow it to run according to the dash switch selection. My fan (1976 450SL) was doing the same thing and I found some random video on the Internet where some guy demo’d the work-around.
Thanks for the info...That might be the answer. I will give that a shot..I have a feeling the blower switch is bad too and I can't find a reasonable blower switch out there.
 

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Discussion Starter #13
Search Heater Blower unit tutorial by GluekAuf in 2010. It's in the Sticky section in climate control (well down)i
Holy Cow I found it ...Thanks !! My fan sounds fine it just will not shot off lol There are a few relays that are above the fuse box....It looks like the harness from the fan motor goes through there but waiting for a wire diagram to see if that could be the answer. Thanks again for your help!
 

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1973 450 SL
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After watching that video and seeing rivets that he drilled out, it may be worthwhile looking at the pins from the bottom. Perhaps there is only a lip on one end allowing you to push the pins from the bottom without having to drill or grind.
 

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Discussion Starter #17
After watching that video and seeing rivets that he drilled out, it may be worthwhile looking at the pins from the bottom. Perhaps there is only a lip on one end allowing you to push the pins from the bottom without having to drill or grind.
Thanks...I watched that video and a few others The 76 SlL is slightly different. There are no lower screws and each switch has a collar you unscrew. My switch had screws but no signs someone drilled out the rivet.
When the switch is removed the fan still runs all the time. I took the back of the fan plug off and only 7 of the 8 pins connect to a wire. I will try to see which has current when the key is on and switch removed and maybe I'll find the source of the power. Ive heard of anti freeze circuit.....well see Thanks for your help!
 

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'72 450SL, 107.044-12-000422
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Check out “Wiring diagrams by rockcrusher” in the EGv107.


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