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View Full Version : Forcing Low Speed Cooling Fan On - Best Practice (or good enough)



Mike8675309
08-28-2005, 12:09 AM
As many know, the issue with the two speed cooling fan on our cars is that the low speed winding must not be energized while the high speed one is.

Thus if you cut #14 and your car still gets hot, it's possible the EEC will turn on the high speed fan while you've got the low speed fan forced on.

This means you'll need to take control of the high speed as well and maybe do all this manual with switches.

There's a good diagram going around that shows how to wire this with thermostatic switches and a couple relays. But if all you want to do is make sure the low speed is off when the high speed comes on, you can do this:

In the picture below you'll see that #14 is cut and a jumper has been run from the IRCM side of #14 to a 3M tap into line #17. Thus when the EEC-IV "grounds" #17 to turn on the high speed fan, this ground will shut down the low speed winding. The once the high speed fan goes off, it'll start the low speed fan again.

http://i8.photobucket.com/albums/a23/tcw_fort/EntryModule/cutwireground.jpg

Joisey Jim
08-29-2005, 12:38 PM
That's exactly what I do during the summer months. I cut # 14 and put connectors on the wire ends, so I can re-connect it during the winter. But when disconnected I hook the IRCM end of #14 into a 3M slice on #17; so that the low speed is shut off when and if the high kicks in. Interestingly with the low running all the time the gauge rarely goes beyond N. I was also thinking about adding a switch in line for the low speed for the 'in-between' months.

sizemoremk
08-29-2005, 01:13 PM
Hmm, never thought much about that!

But to my knowledge, my high speed fan never comes on... Even with the old factory radiator, I seem to have a freakishly cool running SC, or the guage is BAD off... If I'm in traffic, I'll see "O" maybe a little "R" if really, really bad...

Either way, I just tapped into the EEC wiring for this, and I have leads from both low and high pins... I got the ashttray panel switch, and am hoping I can find a 3 way switch to fit in nicely.

From what I read, you can ground either pin 41 for high, or pin 55 for low.

I wanted to be able to run the high speed in short bursts at the track to cool things down, but I would hate for it to turn on the low while I cheat the high one on.

I assume that with a 3 position switch, and I don't cut the wire, then they could both come on....

Now I am curious how I can prevent this? Without cuttin the wires...

If I did cut the wires, and went to "maual only" control, would this throw a code or something??? I know it turns the fan on when I pull the codes???

BTW, here is one of the threads with diagrams...
http://www.sccoa.com/forums/showthread.php?t=47159&page=1&pp=10&highlight=eec+pinout

Thanks!

Joisey Jim
08-29-2005, 04:39 PM
Mike - you could simply put in a switch and just ground #17 to run the high speed fan for short bursts. The only problem is the high amp draw when the low speed wasn't running first. The old MN12 "Cool Fan Switch" did that by running/grounding it thru a 200 deg sensor attached to the rad. However, on '89-93 SC's it's probably ok, because the fan is powered using a fusible link; but on '94/95 you'd probably blow the fuses or worse (I melted mine and ended-up having to install a fusible link). Hence I just cut #14 and let the low speed run all summer.

Mike8675309
08-29-2005, 06:00 PM
I'd throw a splice on to the high speed wire and wire it into a switch so you can ground it. Then turn the A/C on just after a run for a few seconds, then flip the switch. That'll turn on the high speed fan and you can shut the a/c off then.

That'll help with the load.

Doing this won't throw a code as the EEC doesn't sense the fan running, only triggers it to run.

Anyway, if all you do is tap the high speed line you won't even be interrupting the normal operation of the fan.

trife86
08-29-2005, 07:31 PM
i once cut wire #14 to try this but for some reason that fan ran all the time, even with no key in ignition :confused: but since than i got a new ircm

Mike8675309
08-29-2005, 08:18 PM
Yeah, if the fan runs even with key off, there's a failure in the IRCM that's shorting power into the relays. The module has a 12 volt source with key off but it shouldn't be switching any relays without EEC control. Their fail safe mode is off. For them to be on either the EEC is flipped out, or the IRCM flipped.

It sounds like you figured out which one was the culpret there.

shawpdx1
06-28-2006, 12:03 PM
now thats a good pic I understand it now

XR7inWI
06-28-2006, 12:54 PM
Someone care to fill me in here why it is necessary to cut #14, tap into #17 and all that jazz? I just leave my defroster on with the blower fan set to low and temp to cool (or wherever I need it depending on outside temps) and that forces the fan to run all the time when going under 40 MPH. Over 40 MPH and the fan kicks of because it is not needed at higher speeds and if the coolant temps should happen to get high enough the high speed fan kicks on like it should.

No wires to cut, no splices to make, no switches to wire up and/or mount. The ONLY thing I needed to do was jumper the connector on the AC accumulator and unplug the AC compressor because my AC is junk and will soon be removed.

Even on hot days with outside temps in the high 90's, my XR7 runs cool as a cucumber.


:confused: Confused XR7inWI :confused:

90blkbrd
06-28-2006, 12:55 PM
Hmm, never thought much about that!

But to my knowledge, my high speed fan never comes on... Even with the old factory radiator, I seem to have a freakishly cool running SC, or the guage is BAD off... If I'm in traffic, I'll see "O" maybe a little "R" if really, really bad...


FYI
I have had my SC for about 3 year now. The first 2 years the temp guage would hover around N and almost never go higher. Then late last fall it it would barely read anything. Put in a new sensor and now it gets to R when it is fully warmed up.

90blkbrd
06-28-2006, 12:57 PM
I'd throw a splice on to the high speed wire and wire it into a switch so you can ground it. Then turn the A/C on just after a run for a few seconds, then flip the switch. That'll turn on the high speed fan and you can shut the a/c off then.

Does the A/C turn on the high speed or the low speed fan?

If your A/C is missing or discharged, the fan won't kick on, is there a way around this? I would like to just press my A/C button and get the fan to run.

XR7inWI
06-28-2006, 01:25 PM
Does the A/C turn on the high speed or the low speed fan?

If your A/C is missing or discharged, the fan won't kick on, is there a way around this? I would like to just press my A/C button and get the fan to run.

read my post above.... ;)

90blkbrd
06-28-2006, 01:36 PM
read my post above.... ;)

Tracy,

:o Sorry about that. Somehow I completely missed reading your post.

Now I just need to figure out where the AC accumulator is...:rolleyes:

XR7inWI
06-28-2006, 01:50 PM
Tracy,

:o Sorry about that. Somehow I completely missed reading your post.

Now I just need to figure out where the AC accumulator is...:rolleyes:
Passenger side back by the firewall. Follow the AC lines ... they run right to it. Pull the plug on top of the accumulator and jump the terminals in the PLUG with a jumper wire. Fan should come on whenever key is on and defrost or AC is switched on.

As for high speed or low speed being on when defrost/AC is on.... I had always ASSUMED it was the low speed. Can anyone confirm this, or confirm that I am wrong?

90blkbrd
06-28-2006, 06:14 PM
Passenger side back by the firewall. Follow the AC lines ... they run right to it. Pull the plug on top of the accumulator and jump the terminals in the PLUG with a jumper wire. Fan should come on whenever key is on and defrost or AC is switched on.

As for high speed or low speed being on when defrost/AC is on.... I had always ASSUMED it was the low speed. Can anyone confirm this, or confirm that I am wrong?

Sorry, Tracy I was trying to be sarcastic and I still got the answer. :D

This does work, I just did it. Anyone following this, please note that it did allow the compressor to engage. I don't know what it could hurt, plus it would have to waste hp. So if you use this idea. Just unplug the electrical connector on the top of the compressor and it won't engage.

Please note: On my SC it will only come on when the car is running. It wouldn't run when the car was on accessory or on, but engine not running. I could turn it off and on with the A/C button.

Thanks! This solves my wanting to control the fan and get some extra cooling, at least until I spend some money to get the AC fixed. Knowing me that will be when pigs fly.

joker77_2005
07-21-2006, 10:11 PM
on my 92 i found that when i cut the #14 wire the low speed fan cam on,then if i turned the ac on then the hi speed fan would come on with no problems

Mike8675309
07-21-2006, 11:22 PM
Did you read this part?


As many know, the issue with the two speed cooling fan on our cars is that the low speed winding must not be energized while the high speed one is.

Thus if you cut #14 and your car still gets hot, it's possible the EEC will turn on the high speed fan while you've got the low speed fan forced on.

JL_Bird
09-07-2006, 02:43 PM
Hello SC'ers, first time poster here. Love the board. I don't own a SC, but I just did a complete build on one for a friend, so I was here looking stuff up ALOT :) Gonna do a 5.0 T-bird for myself this winter though.


That wouldn't be very hard to wire that up with a relay of your own. Use a DPST (5 wire) 30A relay to divert the LOW wire on the fan to the HIGH side. When wired like in the picture with the proper relay, when the relay is not activated it allows the circuit to work like normal. It also allows the computer to think it's switching the fan properly. Sometimes wiring a wire that's connected to the computer to a 12v source can cause problems with the computer. The other good thing is that the relay will only draw >300 milliamps, so the wiring going to the dash switch can be very light guage. This will work, trust me, I just wired remote door locks into a reversing polarity system. To really make it neat you could cut both sides of the fan connectors on a junkyard car, and use them to splice it in for that factory look.

Here's the factory schematic and then my idea:

decipha
06-30-2008, 07:36 PM
I did the exact same thing except my a/c works and i need it down here in new orleans so i ran my compressor clutch to a relay, that way when i want my fan on and my compressor off i just flip a switch and voila no more a/c. then if i want my a/c i flip the switch off and presto!

this is a very worthwhile tip and i felt it needs to be commemorated. Thus I am officially calling this the "XR7inWI a/c fan mod"

mods should sticky this


Someone care to fill me in here why it is necessary to cut #14, tap into #17 and all that jazz? I just leave my defroster on with the blower fan set to low and temp to cool (or wherever I need it depending on outside temps) and that forces the fan to run all the time when going under 40 MPH. Over 40 MPH and the fan kicks of because it is not needed at higher speeds and if the coolant temps should happen to get high enough the high speed fan kicks on like it should.

No wires to cut, no splices to make, no switches to wire up and/or mount. The ONLY thing I needed to do was jumper the connector on the AC accumulator and unplug the AC compressor because my AC is junk and will soon be removed.

Even on hot days with outside temps in the high 90's, my XR7 runs cool as a cucumber.


:confused: Confused XR7inWI :confused:

talonhead
06-30-2008, 08:45 PM
Ever since I got my aluminum radiator from mike38sc, I haven't overheated. To the contrary, ....It stays in warm up mode most of the time! The temp gage starts to climb gets to about 185-190 (180* t-stat) and then dives to the left. Have to put a partial block in front of the rad to keep temp up to keep it from running rich! If I install the FMIC this will be great.

MikeH

decipha
07-02-2008, 10:03 PM
remember, efi cars usually come with a 190 t-stat to reduce cylinder wear, its proven that aluminum block engines that run below 180 degrees for extended periods of time have significant cylinder wall wear compared to similiar engine ran above 180, all other factors being the same.

fturner
07-02-2008, 10:07 PM
remember, efi cars usually come with a 190 t-stat to reduce cylinder wear, its proven that aluminum block engines that run below 180 degrees for extended periods of time have significant cylinder wall wear compared to similiar engine ran above 180, all other factors being the same.

Last time I looked our motors had cast iron blocks.

Frit

Parker Dean
07-04-2008, 12:34 AM
on my 92 i found that when i cut the #14 wire the low speed fan cam on,then if i turned the ac on then the hi speed fan would come on with no problems

Interesting. My 90 would run the Low fan unless the engine was too hot, then the High would kick in. When I had a decent radiator it never got hot enough to require the High fan even on 90+ degree days with the A/C on. The blade on this one was slightly unbalanced and you could definitely feel the High speed operation along with hearing it. Much louder, verging on "~~~ is that?" category.

One thing I did notice is that with a following wind, usually 20-30+mph from the S-SE around here, the car would run hot enough to engage the Low cooling fan at freeway speeds. I could tell it was doing that because I knew when it would turn the fan on just idling, and sure enough, when the gauge got to that point the temp would start dropping until it reached the point I knew the fan would cycle off. It would repeat the cycle until you changed directions. Into, or crosswind, was no problem, only with a following wind would it do that. I eventually got tired of worrying about it and wired in a simple switch on wire 14. Switch closed and the EEC had control. Switch open and the fan stayed on in those following wind/freeway speed situations.

decipha
07-04-2008, 12:49 AM
swell, disregard my comment then.. thanks frit, i never knew that, that explains why they can take the abuse i give em :)


Last time I looked our motors had cast iron blocks.

Frit