I have my 1995 FD Cooling fans off the car and am testing them on the bench.

I understand that there are 3 fan speeds.
these speeds are altered by providing power to one or both of the +12 inputs, and the 3rd speed adjustment is by grounding the second ground line.

^^^ This is according to the schematic - but I don't get how the 2nd ground works^^^

Now, I ground the main ground terminal, then apply +12 from the battery to the 1st +12 input.

Fan runs at Speed "X"

Then, I then apply a second +12 from the battery to the 2nd +12 input.

Fan STILL runs at Speed "X"

Now, I ground the 2nd ground terminal, in addition to the first, and apply +12 from the battery to the 1st & 2nd +12 inputs.


Fan runs at a speed SLIGHTLY faster than speed "X".

No other combination of grounds and +12v applications cause a speed change.

In fact the Schematic and the FSM test procedure seem to be in conflict with each other. How can terminals getting +12v in the test procedure show as being switched grounds in the schematic?!

In fact, when I perform the test procedure, putting +12v across the two GND terminals sparks and causes humming in the fan! NOPE - NOT doin' that again.

Furthermore, what orientation are these fan terminals in during the test?
How am I supposed to know for sure where to place the permanent ground terminal?

I checked the car harness, and found the ground, and of course used that on the appropriate terminal on the fan, but I still don't get the results the test claims I should.

Check out the images (attached)


Note the switched ground vs. the permanent ground terminals and there are only 2 +12v terminals




This test procedure does have a switched ground terminal, but ONE of the positions shows one of the grounds getting +12v!!!????





What gives?

 

There might be some useful information in this post, https://www.rx7club.com/3rd-generati...ntrols-876767/

Looking at the schematic it looks like the black wire ( upper left in the plug ) is one ground and the L/O ( lower left ) is the second.
but i would definitely read through that post from arghx, and i think there is one from Dale Clark as well.

 

Thanks MSilk, but already been over all those posts too.

Nothing explains the test procedure above vs. the schematic. Doesn't seem possible.

 

What exactly are you testing them for?

 

Proper operation.

I am diagnosing a chronic overheating issue in summer.

I just exploded my AST.
The engine is less than 5 years old and meticulously cared for.

I cannot figure why this happens every year

 

I'm guessing you've replaced your stock ast can with a better aftermarket one?
What are the symptoms that you are getting that your fans are not working properly? Do they not turn on when they are supposed to? Do they work only on one speed? The thing is that if they are spinning freely once you give them the right positive and negative they are operational. I would be more concerned with the 4 relays. They might look good, even operate but no conductivity once they open, ask me how I know .

 

I am checking the whole cooling system, end to end.

relays are perfect. tested.
Fans were next to test - then this confused mess in the books happened.

 

Ok I don't know if this is any use but:
Fan 1

Harness: Fan:
Yellow+ ~ Blue+
Black- ~ Yellow-
White+ ~ Green+
Red- ~ Black-

Fan 2

Harness: Fan:
Yellow+ ~ Blue+
Black- ~ Yellow-
Red+ ~ Green+
Blue/red- ~ Black-

 

Yep, that's precisely what the books i have here say.

However nothing squares the test procedure with that wiring diagram.

 

Could be also something up with the recall stuff for the cooling system. Thankfully i didnt have that.

 

You need the relays hooked up to get the different speeds. If you are just applying power to the fan wires it won't work right.

 

What about dropping the fans back in the car and using a jumper to jump the cooling relays 2 and 4, which should give you low. Then try jumping relay 3 ( while 2 and 4 are still going ) should be medium, then jump relay 1 which should give you high. I have only started reading on how the fan system works last night ( because of this thread lol ). If you still only get one speed then it would be a fan issue, if you get a combination of speeds then you would have a bummed relay. As for how and why they switch a ground, I have a theory but I am at work and my car is at home so i can't test it.

 

Also, I think the higher speeds are attained when it's getting 12v from multiple sources. One 12v input = low speed, 3 12v inputs = high speed.

Dale