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General Category => Tech - Help Area => Body-Interior-Electrical => Topic started by: remingtongoose77 on December 28, 2017, 09:18:57 PM

Title: factory electric fan issue / help
Post by: remingtongoose77 on December 28, 2017, 09:18:57 PM
Hello,

I'm putting my HD back together and in the head light wiring harness under the radiator core support in about the middle of the harness right below the transmission cooler I have an un-used female connector. I believe this is for a factory installed electric fan.

My particular truck did not come with an electric fan, but my wiring harness has the connector for one. I ordered the factory fan, mounted it and plugged it in. I'm not ready to start the new engine yet so I cannot test my theory, but I was wondering if anyone else has the fan right from the factory and if I am correct on this.

Any fan / harness / or help is appreciated.

Title: Re: factory electric fan issue / help
Post by: ED-NY on December 28, 2017, 10:04:15 PM
The only wire I remember close to that area was for a horn ;)  But sounds like the connector was compatible with the fan?

What color and gauge is the wire, if it is a fan circuit it should be fed power by a relay.

In my experience with TPI and TBI engines the fan relay is supplied with a ground signal from the ECM which trips the 12v power to the fan.  Do you know which ECM the truck has to determine if the ECM even has a fan signal outpout?

I'm surprised that you have a single wire OEM fan...the ones I have worked on (IE F Body) have both 12v and ground and on a two speed fan three wires.  But again this is a 3500HD.

Try tracing it backwards & in the meantime you can always first test it for ground -or- power with key on. If it is a fan circuit probably won't have either because the signal won't be delivered until the temp range is met.


Title: Re: factory electric fan issue / help
Post by: someotherguy on December 29, 2017, 08:48:22 AM
Should be a 2 wire connector if it's for an aux fan, 1 wire for horn since the ground comes through the horn bracket.

The temp sensor for the aux fan is separate on older models, for example on the big block it's on the passenger side head, with the dash gauge sensor on the driver side head.  I believe at some point fans moved to being triggered strictly by the PCM and they did away with that extra sensor but that's some vague memory talking.

On my old black HD project which was a '94 that I converted to the newer engine/harness/etc. with parts from a '96, the aux fan connector wires are light blue and black (or maybe dark gray?) - here's a pic:

(http://www.someotherplace.com/bb/proj/35hd_119s.jpg)

Richard
Title: Re: factory electric fan issue / help
Post by: remingtongoose77 on December 29, 2017, 09:45:08 AM
Thank you guys for the info,

I have a weird set up. I have a (2) wire horn connector, its hooked up and connected. The fan connector is also a (2) wire and I believe the colors are red and black.

I should trace them back, the wire gage did appear small to me to be a fan, I will check that out. I don't recall seeing a "fan relay" in my relay / fuse box. I'm not sure what this connector is for if its not for a fan.

Worst case I can run my own relay and either trip the relay with a switch or a thermister.

Thank you.
Title: Re: factory electric fan issue / help
Post by: someotherguy on December 30, 2017, 05:40:12 AM
Does the pigtail come out at the same point shown in my pic?  That harness is from a '96 7.4 truck, although it was a 3500, not a 3500HD.

Richard
Title: Re: factory electric fan issue / help
Post by: remingtongoose77 on January 07, 2018, 09:12:53 PM
Yes, my harness looks just like yours.

I sent my ECU off to be tuned by Ed Wright from his company "fast chip". He has been very helpful with questions that are computer / engine specific and he thought the electric fan was not an option in 1996. In addition when he tuned my computer he thought there was not a provision for an electric fan.

Thanks guys,

Goose
Title: Re: factory electric fan issue / help
Post by: someotherguy on January 08, 2018, 09:47:51 AM
That fan was original equipment on the 1996 C3500 dually that I pulled the 7.4 engine, harnesses, pcm, and many other parts from to convert my 1994 3500HD from diesel over to gas.

In 1996 it wouldn't be controlled by the pcm; pretty sure it's just a switch and relay arrangement, with the temperature sensor acting as the switch - though I never studied the wiring close enough to know for sure.  I believe it wasn't until the later 1990's before pcm control of the aux fan became a thing, and they eliminated that second temperature sensor over on the passenger side head.

Richard
Title: Re: factory electric fan issue / help
Post by: ED-NY on January 08, 2018, 10:51:46 AM
If you have the PCM service number ...might be able to locate a pcm pin out to see if it has a fan signal provision.
Title: Re: factory electric fan issue / help
Post by: ED-NY on January 08, 2018, 12:15:34 PM
According to my Engine Control Module Wiring Diagrams and Pin Identification manual you have an Auxiliary Fan Relay circuit:

#6 on the Black 24 pin connector, circuit #473  DK/BLU wire (see attached)

Title: Re: factory electric fan issue / help
Post by: ROAD on January 08, 2018, 12:38:10 PM
   That fan is in place to keep the head pressure down in the ac compressor. And is controlled by the high pressure switch in the high side line on top of the ac compressor. unplug  the connector and jump the plug the  fan should come on if all relays and fuse are good.
Title: Re: factory electric fan issue / help
Post by: someotherguy on January 10, 2018, 12:04:37 PM
   That fan is in place to keep the head pressure down in the ac compressor. And is controlled by the high pressure switch in the high side line on top of the ac compressor. unplug  the connector and jump the plug the  fan should come on if all relays and fuse are good.
While you're right I think that's only half the story.  In general those aux cooling fans are designed to come into play in two scenarios - if A/C compressor head pressure reaches a certain threshold, OR if engine coolant temp reaches a certain threshold.  I could be wrong...but memory tells me this is the case in most of the arrangements and is why the engines in the vehicles I was working on had a secondary coolant sensor in the passenger side head.  Otherwise they would just have a pipe plug there.

Richard