Grumpy

What you might consider doing is not using the ecm to control the fans.
I just use a radiator fan switch from a 87 GN (on@210).
In case you haven't noticed, the ecm is used to ground all the items that it drives (with rare exception), so there is good reason for them to run warm. What I perfer to do is releive them of as much heat as possible so they don't run as hot. To date I have yet to need to replace an ecm other then for wearing out the prom socket.

P J Moran

Does this switch have the proper "socket" to accept the F body connector?

------------------
'87 IROC 5.7l TPI - original owner!

Like a ROC 89

I am running the exact same switch as Grumpy and it plugs right in. It IS the exact same connector but turns on the fans at 203degrees instead of 240degrees like the stock switch. It also costs only $25 unlike the Hypertech or Jet switch which costs almost $50.

[This message has been edited by Like a ROC 89 (edited June 04, 2001).]

ANDYZ28

Is there any chance you might have the part# for this switch? It would be a big help.

Thanks, andyZ28

Brent

iTrader: (1)

3053190 is the number. It also was part of the ZZ4 fbody kit.

3.8TransAM

This will get buried and forgotten :-)

I run my primary thru the ecm and the secondary using the GN fan switch since i was into F-bodies.. It always comes up and 5 min later someone needs it again :-)

Also elimiantes some ecm control of at least one fan , a good cooling sstem and one fan can support a hopped up 350 in bumper to bumper traffic, least for awhile

later
Jeremy

dimented24x7

iTrader: (2)

The only thing I really dont like about using the ecm for total fan control is that, in the event of a hardware, overvoltage, or prom failure for me, there is nothing to control the fan. Having a secondary fan thats on its own system provides redundancy. Im using a relay that has a 75 Ohm solenoid coil so heat from current draw isnt a problem but if something goes wrong with the ecm I have to physically get out of the car and ground the relay to turn on the fan.

ANDYZ28

When I rescued my '82 Z28 from oblivion I was faced with this question also. I converted the car to serp belt drive, and dual fans. The only way I could control the fans was through the ground side of the fan relays, ie; coolant temp switch closes (and provides a ground path) at 205 degrees and off at 195 degrees turns BOTH fans on. Thanks to a swell guy at a local Pontiac dealer I found an A/C switch that is normally open, as A/C pressue rises the switch closes and both fans run. It has worked great for 3 years now. But I don't have an ECM anymore, the previous owner ditched it.

JPrevost

Find me a switch that does on at ~185 and less than $30 and I'll buy it. I just haven't found one to come on that low and it's annoying because my motor likes to be between 170 and 180.

Grumpy

And the same can be said for injector control, the O2 for closed loop, the K/S for detonation, etc..

A simple on-off switch would give redundancy.

Grumpy

Wire in a $3 RS on-off switch, and send me the remaing $26.99.

And why does it favor 170-180dF?.
Sounds to me like the cal, is off.
It seems to me, that's it's been pretty well documented, that warmer temps are in fact better.

JP84Z430HP

Doesn't the ECM kick on the fan by default in most of these cases? Besides, if the ECM has a major failure, you're likely not going to be able to drive the car all that well anyway....

AndyZ:
Do you happen to have a part number for that A/C switch? I'm guessing that it's a high pressure switch from the way you're describing it, which is what I've been looking for.

In the future, I plan to use a pressure transducer such as what the "W" cars used to control the fans on and off by pressure, but that's a while off yet.

dimented24x7

iTrader: (2)

I still have the F/S, its jsut not connected. Simply reconnecting it would allow the fan to run if i needed to keep driving. Ive had cooling system and fan failures from hardware problems before so nothings immune to failure. Best defense is to be alert to whats going on.

JP84Z430HP,
The fan was an afterthought. Wanted more control over how it worked so I dropped in some code into the computer and wired it up.

dimented24x7

iTrader: (2)

That requires that the user actually activate the fan. I just want to get in the car and space out like I usually do when Im driving. :O Did I say that? No officer, I was paying complete attention to the road.

Im likely not to remember to turn on the fan. For the lazy, automation is good...

whitess

Grumpy,
Does the GN switch work just for the single fan setup or duals or both? How did you wire it up?
Thanks,
Larry.

Grumpy

When I want cooling, I turn every thing on. I can't see the point of partical cooling, other then when doing condenser cooling.
So it's just wired up as the fail safe for the ecm, per stock, and I have a manual over ride.

MikeT 88IROC350

Hayden makes a brass radiator thermal switch that closes 185/opens at 170. P/N is 3652. I use this switch in parallel with the stock switch to turn on just the secondary fan. Of course I have the usual manual control switch wired in. I use the ECM to just control the primary fan, set to 185/183. The Hayden switch works more like 190/180. This way just the 1 fan can keep the engine cool, except on really hot days, or long idle periods, the Hayden kicks in. The fan motors take big power to run, so if I can keep engine cool with only 1 fan, the better.

By the way I am running 170 deg Tstat, and car normally runs 170-180.

Guest

Hayden also makes an adjustable control with a probe that goes in the radiator (3647). Can set it to just about anything you want. Not that expensive, and they hold up pretty well. I have 3 cars with them, only one of them in 10+ years I've had them has failed and it was pretty easy to repair.

Could also visit this article, that Willie wrote up years ago
https://www.thirdgen.org/newdesign/tech/cool.shtml

DAVECS1

iTrader: (2)

I guess I do not understand how a sinking drive running the switching side of a relay can produce wear and tear on your ECM. I am using two Potter and Brumsfield high current relays to run the flexlite 4600CFM setup without using the costly mosfet controller, Flexlite suggests using. I have yet to encounter any problems. I am still using the original 91 730 ecm, and changing bits in my own chips allows me to set fan temps were ever I want them.

MrBill

Whether a current driver sources current (provides voltage to a grounded load) or sinks current (provides ground path to a powered load, like a typical ECM driver)...direction of current flow doesn't matter. The absolute value of current flow (be it positive or negative) ultimately determines how much power is dissipated (heat). The main reason you find current "sink" drivers (like an ECM driver) is that you can tie two or more of them together in a "wired-OR" configuration without damaging the drivers...not that you would ever really want to in this case. Also if a wire happens to develop a short to ground (through a worn firewall grommet for example) it won't damage the ECM.

Jon (or anyone else), if you want to build an adjustable fan switch controller let me know and I'll send you the schematic. It doesn't take many components, pretty easy to build. I've been running one on my car that I built with perfboard right after I bought it ('bout three years now)...hasn't failed yet and it lives under the hood. It has about a 5-degree "window" between on and off. Right now mine turns on at 200 off at 195, adjustable with a pot.

JPrevost

That would be useful .
Which sensor does it use?

MTPFI-MAF

I would like a schematic.

Grumpy

Gessh, Doc's been waving his hands, all morning over this, guess we'll need to have a set if it's not too much trouble.

MrBill

Here's what I'm using:

http://misterbill.homeip.net/vette/F...EMATIC_3_0.PDF

I pondered having some boards made...just didn't think there would really be any interest.

Let me know if anything doesn't make sense.

MikeT 88IROC350

I know about the Hayden adjustable control relay. I bought the Derale version (p/n 16759) last year and have yet to put it in. You can adjust the turn-on temp, but the OFF temp is like 15 deg lower than the ON temp. I think the Hayden is the same way. The earlier versions of the Derale had 2 pots on the control, 1 for on temp and 1 for off temp, which was 2-20deg below turn on temp. I am sure both units would work fine. Just that I use my ECM to control the primary fan, and the simple 3652 switch to control secondary fan. Just got to play with on/off temps for the primary, in order to make it all work togethor. Plus I think the thermostat selection is a big part of the system.

Mr Bill, that is a sweet setup you got there. I like how you tap off the existing cooling temp sensor. No guessing what temps you want the fan to switch. Just look at what the ECM sees and adjust accordingly! It looks like you just use the 1k pot (R4) to adjust the switching point? I would suggest adding another pot, to be able to adjust the turn-off temp. May have to add some more resistors, but that would be sweet.

DAVECS1

iTrader: (2)

I realize it does not matter which direction the current is going, I guess the point I was trying to make, was the fact that a relay switching load is in the vacinity of 300-400 mA. Is 300-400mA really going to toast an ECM?

I guess another thing I do not understand, is sounds as if the ECM may not turn the fans on exactly at the specified temperature requested. Am I understanding this right? I gues I could get off my chair here and set up a thermal couple with a digital readout and figure out how far it is off. I know there are easier ways, but if you have the tools why not use them.

MrBill

Mike, actually I'm not using the CTS (ECM temp input), I'm using the temp gauge sending unit. No reason you couldn't use the CTS though as long as you know the volts/degree transfer. The other option is to use a stand-alone sending unit just for the fan controller, which I actually like better since the transfer is a lot easier to figger out, plus that setup would be more accurate (not that accuracy is real important).

Yes the 1K pot moves the on/off "window" up and down. I didn't make the window size itself adjustable, didn't really see a need to. The way it is set up now you get about a 5 degree window between on and off, seemed good enough to me.

Dave, no that kind of current should pose no problem for the ECM.

Grumpy

Doc says, simplicity is the key to design, and asks anyone to do better then this.

+_____/.____O___>>>
................Fan

He's been a real PITB today.........

Come to think of it, if you do some boards, I'll take $20 worth.

11sORbust

How much heat could the grounded output create,really? It's not like the ecm drive 12 volts to the fan(s). It's just grounding the fan relay, and that is external....

IMO, running a thermo switch to control fans is not the best thing. The switch is a moving part that can wear/fail vs the ecm that does things electronically(no moving parts). Sure it's still based off another sensor(CTS), but if the cts fails you'll notice it well before the thermo fan switch. Another thing that suppports my view is that I have seen many cars with the fans on all the time and the ecm never failed. That's after YEARS of running always on..

But what do I know.....

dimented24x7

iTrader: (2)

As long as the current isnt excessive they wont get hot. I mistakenly hooked a resister that was too low up to one of the outputs, which was due to me not wearing my glasses when I was looking for the right one, and it smoked the resister. Didnt get real hot, though. The driver only got to like around 120 deg. IIRC, theyre rated to something like 600 mA per output. Most relays usually have a solenoid coil with a good deal of resistance so they wont draw alot of current when theyre active.

TheMysticWizard

iTrader: (1)

So this switch in the pass. side head will turn my second fan on at about 205*f... what temp does it turn it off at? Will that work good with a 180 thermostat?

I was planning on setting up the PROM to turn the primary fan on at 195 and off at 185. Does that sound too cool for a 180 stat? Maybe I should try and find me a 170 stat? What do you guys think?