Cooling Fan Update


Created: 7/17/1997 12:00 AM

Last updated: 8/16/03


Author/source: DML/Swingle


To: dmcnews submit

Dave S.

Cooling Fan update. The reference for this was Darryl Tinnerstadt's document that is now published in "DMCNEWS - The 'Zine". I decided to change this around a little more because I didn't want to disturb the original relay sockets and wiring, and I wanted to keep the reversed functionality of the Cooling Fan Fail light that I had previously hooked up. That is, the light goes ON when the fans run. Darryl mentions using P&B relays for replacing these and the other Lucas (or Bosch) SPST relays. P&B also makes sockets for the relays (part number VCF4-1002), and socket terminals 26A1348B (14 gauge) and 26A1348C (12 gauge). These sockets will interlock with the DMC relay sockets and look like the factory put them there. I installed two new sockets adjacent to the green Rear Defroster relay socket. I wired them to the old cooling fan socket and fan fail socket in the manner of the original fan fail bypass, i.e. by plugging standard spade lugs into the sockets and making direct connections to the 40A breaker. I now have a separate relay for each fan, and the wiring could be put back to original by simply unplugging everything and putting the original jumper and relay back in.

To make the Cooling Fan light work, I made up a simple transistor switch circuit that bridges both cooling fan power leads at the fan fail socket. If either of the fuses feeding the fans blow, the light will not light up. I also made the wiring change so that the fans run constantly with the A/C on, this also provides a handy means to check the cooling fan operation. If the "Cooling Fan (Fail)" light goes on with the A/C on, both the fans are running, or at least getting power. With the A/C on, the compressor still cycles but the fans run constantly.

I plan to draft up a diagram for this when I have some time. So far I haven't had time in the past 18 months.


There have been some postings recently about "my" cooling fan rewire procedure, a conversion actually written by Harold McElrath, and edited and published by me.  Its a very low-cost way to fix the inherent cooling fan overload, one which has been used by lots of owners over the years.  I recognize the other side of the argument, that you should not modify the stock wiring, but firmly believe that if something is designed and built poorly, you should fix it.  While the expensive "plug and play" unit works, it is still a band-aid in some respects - it doesn't correct the error, it just works around it.

Anyway, my newly acquired project car came with one of the "expensive units" still in the box.  I quickly found out why it was still in the box - the car had no fan fail relay socket to plug it into.  Lesson number one - "plug and play" only works if someone hasn't already modified the car.  Without knowing what he had, the prior owner let himself be convinced he needed this unit.  But it wouldn't work in his car.  Lesson number two - and this is important - if you do modify the wiring, clearly document it.  I always glue a properly modified copy of the relay/fuse schematic to the underside of the relay compartment cover.

And if you do choose to modify the cooling fan circuit by splitting the load onto a second relay as my/our procedure explains,  here is lesson number three - think about what you are doing, don't just blindly start changing.  Since this car had already been modified (incorrectly) I went back to my own way of doing it.  Even though these directions have been published and used for well over 10 years, I got out a copy and thought about every step and what it was doing.  And guess what - in spite of lots of people using these instructions over many years without a single complaint, I FOUND AN ERROR IN MY OWN WRITE-UP!

This is what the text currently says: "The cooling fan breaker should have a brown/orange wire from the battery and a brown/slate or black/orange wire leading to the fan fail relay socket." ... "The brown wire mentioned in the paragraph above should also have a new ring terminal added and be attached to the "ACC" terminal of the new cooling fan breaker."   

WRONG.  Brown wires are "hot" wires.  The large brown wire goes to the BAT terminal on the cooling fan circuit breaker; the brown/orange and brown/slate or black/orange wires both now go on the ACC terminal.  So all of you who have performed this conversion, please check your wiring to make sure it is correct (it will work the other way but bypasses the breaker, not something you want to do).  I know the purists will take this as one more reason why you should not modify your wiring.  I like to look at it as someone being willing to admit when he made a mistake and helping to correct it.

And for the cost of one standard relay, I still think its a good way to go.


Darryl Tinnerstet
Specialty Automotive
McCleary, WA
www.delorean-parts.com




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