I've actually brought this up in another post (see here ) already, but I thought I'd put a more detailed description of their behavior here...

Basically, here's what happens... when I turn the key to ignition position (with the engine stopped and cold), the driver's side fan is always on; passenger's is off. When I start the car, the driver's side fan remains on, and the passenger's remans off. Tonight, however, when the temp gague got up to about 220, the driver's side fan actually turned *off* (and the passenger's stayed off). This leaves me with no cooling after the temp reaches 220, causing the engine to overheat. What's even more odd is that, when I turned the engine off, and then put the key in the ignition position (with the engine still off), the *passenger's* side fan turned on, and the driver's side fan stayed off. Then, I turned the key off, and then on again, and then neither of the fans would turn on. I have no idea what this could be a symptom of--all I can say is that the wiring harness near the battery (leading to the fans) has very obviously been cut before, and that I've done what I could to try to put the wires back to where they belong.

I need to get this figured out, because I'm in the process of trying to break in a rebuilt engine, and having it continually overheat every ten minutes due to the fans acting up is making breaking it in very difficult.

Any ideas? Thanks for any help!

BTW -- This is on an '89 Camaro IROC-Z with the 5.7L TPI engine--all as stock as I can get it.

 

Here is how they should work. The primary fan is controlled by the ECM. When the coolant temp reaches about 220 degrees primary(driver)fan should come on and run until the temp goes down. Primary fan is also controlled by the AC request meaning when AC is on it will turn on. The secondary fan is controlled by the fan switch which is in the block on the passenger side. It turns on the secondary fan relay when the temp reaches around 238 degrees. It is independent of the ECM, and if the engine is hot enough simply turning on the key will cause it to come on. It sounds like a wiring issue to me. Either pick up a Chilton manual and double check color coding of the wireing or check on the site. Look in the tech articles section, Bill Weismann has an article that shows and describes how the system works.

 

You know what it sounds like to me, then? It sounds like my secondary fan must be doing what it's supposed to (because I've never seen it come on unless the temp gague is above 220), and it sounds like my primary fan is operating *opposite* to the way it should (It's on even on startup, but I saw it shut off last night at 220). I have seen one wiring diagram that I got off of the boards (not sure if it's to my car or not), and it looked to me like there are some dual-throw (SPDT) relays that control the fans. Mabye the switched lead has been wired to the wrong pole, making a circuit that should be normally-open be normally-closed? I'm going to check that out...

On a side note, the way the fans work doesn't seem to me to leave very much cooling. Comparing the way the dual fans on my IROC work to the single (but much larger) fan on my '88 Camaro SC work, I bet my little 2.8L V6 gets better cooling than the 5.7L V8 in my IROC. When you think about it, the secondary fan in the IROC should really never have to come on (ideally), because you really should never be operating that hot. So all that leaves is the one small primary fan, versues the one large fan in my '88. Just a thought--I could be wrong, though... I can't imagine that GM would have went from one large fan to two smaller fans if it didn't think two would work better...

Thanks for the reply, Danno! I'm going to go out and see if what I'm thinking is correct...

 

This is the wiring diagram that I got off of the boards. Is it accurate for my setup (1989 Camaro IROC-Z)?

 

Okay, I just found something new out... Instead of the poles being swapped on the primary relay (like I had thought), it turns out instead that the primary relay is on when the ignition is on (which isn't right), and the fan is just comming on as a result. I found this out because my multimeter was giving me 12.05V between the D and F terminals (the relay coil) on that relay with the ignition on.

So, based on the diagram and in my very limited experience with automotive electronics, that tells me that the problem must be somewhere between the ECM and the relay--not between the relay and the fan--right?

I'm still convinced that the primary fan is operating in the exact opposite manner than it should be (based on what it did last night: shutting off at about 220 degrees). However, given that the poles are not swapped, I can't understand why the relay would be getting power when it's not supposed to be and not getting power when it is supposed to be getting power? I'm sure that I could always swap the poles to counteract the inverted operation (double negative), but I still want to know why the ECM would be sending power to the relay at the wrong times...

Any ideas? Or have I missed something here?

 

The F terminal on either relay when it is grounded turns on the relays. The F on primary is the one to look at, that's where the problem is. That wire should go low measuring it to ground when the relay energizes. The AC control head also controls operation of that fan. Check the radiator front, leaves and crap clog it up. Have the fans been replaced, they are puller fans i.e., they draw air in from the front of the car. One guy here had them wired backwards.

 

Danno,

What do you mean by "that wire should go low measuring it to ground"? Also, you say that the A/C control head also controls the operation of the *primary* fan, correct? Looking at the diagram, I couldn't tell that there was any connection between the A/C and the primary system (I was of the understanding that the A/C only affected the secondary fan)...

Anyway, if the A/C does somehow affect the primary fan, then here's something that I noticed: the plug going to the A/C clutch on my car has a diode going between the wires. Something about that just always seem odd to me. Perhaps the previous owner did that thinking that he was doing a good thing? Or is that diode supposed to be there?

Other than that...

a. The fan motors are both new and alike
b. The fans are both pulling air in the correct direction (through the radiator and across the engine)
c. Both of the fan relays are good
d. The secondary fan is working as it should
e. The wiring between the relays and the fans must be good
f. The primary relay is getting power (from the ECM?) when it should not be, and not getting power when it should be

And to complicate things a little more, the primary fan is not even consistient with its dysfunction: putting the car in ignition yesterday (and leaving it there for a while), I noticed that the fan stays on, but then it will cut out for a second, and then turn back on (and continue to do that every now-and-then in irregular intervals).

Sorry if any of this sounds redundant... mabye you've already answered my question, I just need some clarification.

Thanks