Ok, as I don't have the electrical upgrade manual. I need to know how the coil on the main fan relay is energized? Is it switched on, on the negative side, or the positive side of the relay coil? Now, I know that the aux. fan is switched to ground (-) via the block sensor, and the positive wire is hot when the ignition key is switched on. Just need to know the main relay switching + or -. I'm working on a project your going to love, and I think it may even suprise ole' AGENT 86 Many Thanks...

Oh, Lest I forget. Does anyone know the max. current these relays can take, or are rated for???

 

Is it hot when the key is on? Does the main fan run when you manually ground the negative side of the coil?

RACE ON!!!

 

Here's a picture of some typical relays, I know there from my 96 but GM has used this style relay for a long time. Typically I see the coils always being hot and #86 gets pulled low to energize the coil through either the PCM, CCM whatever the case may be or control needed.

They're probably using SCR devices or normal NPN transistors to do the job inside the computer to pull the line low. I never bothered to find out.

BTW, in the picture I scrapped the dash switch, it was totally unnecessary.

 

OK, that is plain as day. Looks like they are running around 50 amps for the motor relays, of course you will have a 80 to 100 amp bump for a milli-second, and 5 amps to energize the coils. No current flows unless pcm goes low. Yes I agree bi-polar, scr, or possibly triac. At first glance it apears you are trying to achieve spike protection w/your wp circuit. I'm interested why they used resistors across the coils, and not diodes?

I am going to be running a heavy relay, that is secondary to the two relays they are using to switch on fans in my 88. I will have to come up with circuitry for the single fan system, that alot of the early vetts had. I was thinking about using PWM switching at high freq. but mechanical is alot more simple, and in alot of cases more reliable. Um, interesting.

I appreciate your time Thanks...

 

Thanks for the comeback. Yes, what you are saying is totally logical. However, I have the car so far apart, it would be dangerous to hook up the bat right now. I believe I have got thing's figured out now. Would still like to see a schematic diagram for the 88. I've got to get that electrical supplement. Many Thanks

 

Sorry. All I have is the one for my 1984 and my main (only) fan is wired the same as your auxiliary fan.


Of course, I had no way of knowing that. You could check it with an Ohm meter.

RACE ON!!!

 

Ya, Sorry I didn't mention that. An ohm-meter is just what I had in mind as well. Thanks...

 

They're using the right fan as a dropping resistor to make them dual speed. Slimey but effective.

When only 11 on the PCM goes low, both fans are in series (low speed)

When 10 goes low both fan are then independent to the source power and ground (high speed)

When what happens or in what order I have no idea. Maybe someone else knows.

I have no idea why they use resistors instead of reversed biased diodes across the coils either. The only answer is they're cheaper? Maybe they are diodes I've never opened one up to look, maybe they just show them as a mechanic would understand, shunting back EMF.

That diode I show was supposed to be on the right hand side of the switch as pictured so that line going to the dash wouldn't be hot at all times and back flow prevention in that direction. Just a little short protection.

The other diode was to prevent back flow to the fuse circuit when a constant 12V was supplied to the relay coil from the dash switch. I scrapped the idea because it's too easy to forget you have the pump on and leave your car. When it's energized only with the key on there's a lot of audible and visual warnings you still have something on. And it's simpler. No switch.

I'm still thinking about the fan circuit and how to switch both those lines, 10 and 11 low but still maintain their independence from each other. Probably two low current relays on both lines with one switch to activate both. Couple of options there and I'm still thinking about the best way.

When you get that schematic I'm interested to see what you're going to do with your relay(s).

 

http://members.shaw.ca/corvette86/Co...%20Control.pdf

 

I see, I didn't study the schematic that well. I can see the motors running in series. That would make a down & dirty way to get the low speed, relay #3 is crucial (interesting). I am doing something very similiar, but in one fan thats armateur has dual windings. I'll show you my very simple schematic when I get it done. Fortunatly, GM has did some of the work for me. Many Thanks...

 

Thank You AGENT 86, Great information. It is interesting how different years use different switching techniques, but I see they are all switching to ground to energize...

 

Sending a ground signal to the low side of the relay coil will allow the 12V to pass through to the fan.

This is all it takes to override the fan as well, just a switched ground in lieu of waiting for the computer to send a ground signal at 228*F

 

Here's a diagram from my 85, also showing where I added the fan overrides.

 

Funny how they show the proper orientation of the shunt diodes in your schematic. But in my 96 schem. they show resistors. Odd. They don't do dual speed either.

 

I noticed that. however on my 88, on top of the relays, it shows a resistor. I do know that would be cheaper, and on a large production scale, could save a million dollars. The system I am designing will be 2 speed, and will fit corvettes with the aux fan for now. I'm doing R&D on it right now. Looks like on low you will see just a little over the stock airflow of the orignal main fan system. I will have to test it to get the exact flows. The front aux. fan will be removed, and on high, this fan system should pull around 3500-4000 CFM (just short of a hurricane . See I am looking out for you vette boy's, and girls. Hope to have the prototype next week, or there abouts. Current pull has been studied, and is very comparable to the stock systems. You may have cooling problems now, but shortly I will be introducing a new weapon in the arsenal (patent pend.). I'm hoping to help, and make a little jingle at the same time. This system will be thoroughly. and rigirously tested on my 88 Corvette. So keep your eye's peeled...

 

Hey CC, thanks for the schematics. I take it, that the fusable links are 20 amps? I will make a few minor changes in that area. Many Thanks...

 

CFM is nice but the SOUND of a hurricane is not. I ran into this on a street truck a while back. I bought the biggest baddest fan I could fit in front of the radiator because there was just no room in back.

Well it cools all right but the noise is deafening. Is it true the shape of the blades has a lot to do with noise and how they are spaced? If you ever look at the old Chevy fans the blades are not symmetrically spaced. The only reason I can think they do this is for noise reduction. Maybe there's a different porpoise I don't know.

 

Harmonics.

 

I'm blueprinting the fan blade even as we speak. Yes, the blade design has alot to do with noise. This unit on high really isn't to bad. I'm just wondering how many time it will kick on high. I think it will be rarely, but will sure be nice to have when needed. I've got a friend of mine that owns a machine shop. He, and I are designing this thing to be one good lookin piece of hardware. My guess is customers would buy it for looks alone. However it will be fully functional. As I am a Vette owner to, and this thing is going on my car, with no worries. should be available in satin, and highly polished aluminum. My brother is a pofessional metal finisher, and lives two block away. Now I need someone to test it in death valley . I am confident, but not over confident. Actually I will probably be giving a couple away to people on the forum, for testing purposes, and get a few more points of view... Ya, I beleive you are right from what I have researched. You would think they would be out of balance...

 

Isn't that a DPST switch? Is there a reason for the double pole switch? Wouldn't a SPST suffice, with no compromise? Two SPST (you COULD use DPDT or DPST) switches would allow for less battery drain, by permitting the running of the fans, individually, between rounds at the drag strip.

RACE ON!!!