I have a traditional mechanical fan on the ol' 406 engine at the moment and want ot swap to dual electrics instead. I found the following thread to help me., particularly post #4.

https://www.thirdgen.org/forums/diy-...dual-fans.html

Rather than risk failure by removing the mechanical fan right away, I decided to test the circuit first to see if I can get to to work. ( I pinned wires to E8 and F8, and hooked up LED's to them, and to a chassis ground. (Pep Boys -dress up type)

I reset temps in the bin for testing as follows
Fan 1 off 170F (76.3C)
Fan 1 on 175F (79.3)
fan 2 off 180F (82.3)
fan 2 on 185F (85.3)

The "flag" is set, check in the box for." Option Word Four- Bit 5 N.O. Fan Request Input"

As you can guess , result: Nada. Nothing. The LED's never came on, neither one. The engine started at 100F, well below qualifier temp.

Where did I go wrong?

One thought was I used 12 V LED's. Is it a 5V circuit from those pins, and therefore incapable of trigger the LED"S to come on. I don't know if they have a threshold voltage that may not have been reached.

 

the ECM grounds the pins to turn the fans on. so the other side of the LEDs needs to go to power.
be sure to use the ECM to control relays as the ECM can not handle the current a fan would pull.

 

GREAT! Thanks Denn! Should be an easy fix then..

 

Next problem to solve.

Now just the opposite occurs.

Red lead from LEDs to power source, black leads to ECM pins E8 and F8 respectively

Both lights come on immediately at "key on-engine off" and during "key on-engine on" and both stay on. So the circuit works, but not like it should that both test lights come on when power is turned on. (.. and therefore so would the fans if it was hooked up all the way)

Ambient engine temps still at air temperature, well below "enable" temps.
Seems strange

 

Are they turning partially on or full on? At key-on, engine-off, ground either pin and see if they get a lot brighter. Leakage current through the q-driver will turn them partially on.

At key-on, engine off, they are commanded off. That is unless in limp mode (main fan turns on), or the AB terminals of the ALDL connector are shorted (both turn on).

RBob.

 

Would there be other symptoms if the A and B terminals were shorted. Like a check engine light always on, or codes blinking?

 

Well yes, shorting A&B, key-on, engine-off is how to blink out codes.

RBob.

 

While rare, a pull up resistor may be need on the ground side of the LEDs, to avoid the drain that RBob was mentioning

I do notice on my test bench, that certain LEDs are on, but very dim, when the outputs are not active, I plan to add the pull up resistors when I rebuild the test bench.

 

at initial key on engine off, on the primary ECM fan control you should see ~2 seconds of fan on.
im not running my secondary fans thru the ECM, i still have them going thru the temp switch in the right head. but i would guess that the secondary fan control on the ECM works just like the primary fan control.
once the motor is running even dead cold, if the ECM sees input from the A/C, it should turn on at least the primary fan, if not both.

as mentioned, there could be some bleed thru from the ECM with the LEDs which may not be a problem with relays.

as far as the relays go, i prefer to use relays that have either diodes or resistors in them to protect against inductive spikes, with resistor types being preferred over diode type relays because polarity isn't critical.

 

Maybe a few trim pots would be helpful. Or I can grab a few different lights from Radio Smack to see if I get the same bleed though. The test lights I spoke of were not the "final" bulbs going into the dash anyway, just a few I had handy, So it bears some research to see if the intended bulbs do the same thing.

Off the subject, it seems like the same names tend to show up in responses whenever I ask a question or have a problem. I am grateful for your service to the forum. . As always, my sincere Thank You gentlemen.

Dave Buchholz
Rochester NY

 

if it is indeed bleed thru (if thats the right term for it) as RBob & Shooter mentioned, pots may do the trick. also since LEDs use so little power, regular light bulbs may work better, of course thats just a guess.

i can't speak for anyone else, but you & i run the same ECM & mask so im able to lend a hand a good bit more than if you had say a 165 or were running code 58 or 59.
im just trying to give back a little for all i've learned from here

 

Hey Lakeffect2 – Was just wondering if you’ve solved your fan issues. Crazy as it sounds, it seems as if A/C has been requested because as RBob stated, fans should not be activated with key-on, engine off (unless in AB shorted Diagnostic Mode)– only with engine on, AC on or temp above ECM-set temps. Also see Post #17 here: https://www.thirdgen.org/forums/diy-prom/587986-need-some-dual-fan.html).

FWIW, I installed dash-mounted LEDs in my fan circuits so would know they were on or off. I used these LEDs with success: Radio Shack #276-0085, 1/4W, 660 ohm resistor for 12VDC operation (power dissipation = 180mW, forward voltage = 12V, forward current = 15mA).

BTW-I have complete relay/wiring diagrams for the ECM/fans/AC/ if you’re interested.

 

I think it has been fixed. The console that the lights will be go in is out of the car at the moment, getting redone. It is getting the Tuneview 2 put in and is not yet hooked up permanently to the ECM. Now that I have the lights powered instead of grounded they seem to have worked independantly. There does seem to be a residual current in them as there is usually a slight glow in them, and then go bright when the temp goes up.

I was using a test bin for a few days. Once the console is back in, I will continue to monitor the lights before actually swapping the fans over. I have the mechanical fan in place still at this point. I have an event to get on July 27 & 28 and don't want to risk them being inoperable, as I am the coordinator of the event, Wagonfest in Geneva NY.

Thanks for asking. Dave