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Rad Fan motor connections

Posted: Fri Jun 17, 2016 2:30 pm
by simmit
The Rad. Fan loom on MB50 has 3 wires going to the motor but only 2 are connected. Is this intended or simply, has one come adrift?
Looked at Peter's excellent wiring illustrations but can hardly read the text and can't find the Fan motor.

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 2:35 pm
by philhoward
I thought the MB had a 2 speed fan - or was I dreaming it?

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 2:35 pm
by peter freeman
My MB fan is a two speed - perhaps yours has been replaced by a single speed fan. Unfortunately we are at the international at the moment so I cannot check things out for you. Peter

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 3:24 pm
by Roger Pennington
Rad fan is towards the top right corner on Peter's diagram and has three wires brown black and orange, and two speeds, operated by two relays (which if I'm reading the diagram correctly, switch the output from the motor?)

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 3:27 pm
by philhoward
It's switching either one or two earth paths. I'm guessing there's two sets of windings in there fed from the common (brown) supply internally. Think of a 2 speed wiper motor but instead of switching the +ve, they switch the -ve instead. It has the same effect electrically.

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 3:30 pm
by Roger Pennington
Black is slow, and orange is fast according to the diagram :)

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 3:42 pm
by philhoward
Yep - that's how I read it too.

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 4:08 pm
by scimjim
simmit wrote:Looked at Peter's excellent wiring illustrations but can hardly read the text and can't find the Fan motor.
Open the wiring diagrams entitled a or b which are better resolution.

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 9:24 pm
by simmit
scimjim wrote:
simmit wrote:Looked at Peter's excellent wiring illustrations but can hardly read the text and can't find the Fan motor.
Open the wiring diagrams entitled a or b which are better resolution.
Thanks Jim, much clearer now. I hadn't realised the a and b were independent links.

My fan motor has 3 connections so probably original and one of the loom connections simply came adrift.

Am currently replacing coolant hoses (found very helpful silicone manufacturer less than 1 mile away and he's knocking out set of hoses for the MB) so not able yet to run the motor and try things out. In passing, my local radiator repair guy is also good egg and put a drain tap in the radiator so I won't get coolant all over the place when next I drain down.

Incidentally, why have a two speed rad. fan and how is it controlled (automatic or manual)? Being new to the MB I'm still finding my way round and further, I claim no electrickery knowledge (strictly clockwork is me).

Re: Rad Fan motor connections

Posted: Fri Jun 17, 2016 10:24 pm
by AJL Electronics
The Otter switch is a two stage device. It switches to earth at two different temperatures, so the fan has an ignition live and two earth feeds switched. Should you fit an aftermarket fan, you may have to use relays to invert it.

Re: Rad Fan motor connections

Posted: Sat Jun 18, 2016 8:09 am
by simmit
AJL Electronics wrote:The Otter switch is a two stage device. It switches to earth at two different temperatures, so the fan has an ignition live and two earth feeds switched. Should you fit an aftermarket fan, you may have to use relays to invert it.
Thanks for the explanation. All good stuff!