I have an '85 C4; it has 2 radiator cooling fans one in front and one on engine side of radiator. I KNOW the front one works (Very well) but have never seen the engine side one working! The car does not overheat (except last weekend driving in 30' heat in first gear over 10k of dirt road with Air con on full - was a club run; don't ask!) I know it would (I guess) be simple enought to run 12v to the fan itself but is there a way to test that the system turns this fan on at all?

 

The cooling fan system of relays and stuff is the most confusing part of the electrical on the whole car. I bypassed mine with just a switch because I spent way too long trying to figure out how the relay wiring works.

Anyways, the fan should come on at 228 degrees. Like you thought, the first step is running 12 V to one side of the fan, and ground to the other, and see if it works. If it does, the next step is trying to borrow(or buy $8) a new relay for the fan, which is located right in front of the battery.

If the fan works but the relay system doesn't, I'd just bypass it.

 

If you open the hi-pressure connector in the A/C line and start the engine the ECM should bring on the main fan (behind radiator); if not replace the relay, as mentioned above.

 

Wouldn't they run automatically when the A/C is turned on?

 

No, on MINE doing that brings on the Aux fan (in FRONT of radiator) :confused:

 

Good point; I didn't think of that because my A/C doesn't work well enough to use. :eek:

 

Main fan (the one behind the radiator) is controlled by the ECM which simply provides a ground based on a 226 degree signal from the Coolant Temp Sensor (below the throttle body on the intake manifold), or when the fan switch (on the high pressure line from the condensor to the evaporator) opens at 230 psi. As the fan cools the a/c charge, the pressure drops and the switch closes at about 190 psi, signalling the ECM to turn off the fan. The aux fan (the one in front of the radiator) is independent of the main fan with a switch in the cylinder head providing a ground when it reaches 228 degrees. If I understand you correctly, your aux fan - the fan in front of the radiator - is coming on with the a/c, and if so, your Vette has been rewired. My guess would be that when it was converted to right hand drive, the Relays got switched with the inputs from the ECM and fan switch remaining intact and the outputs to the fans being switched. Some say a pusher - the fan in front of the radiator - is superior to to a puller - the one behind it - for a/c performance. If your Vette was rewired, the main fan should now come on at 228 degrees, after the aux fan comes on and if your cooling system is operating properly, it probably isn't going to come on as long as the a/c is on and the other fan is running. To test it, disconnect the green wire to the fan switch and ground it on the block - the main fan should come on. On '86 and up, the switch is on the left head between the #1 & #3 plugs (towards the front). On the '84 & '85, the switch is on right head, between the #6 and #8 plugs (towards the rear).

 

THANKS 'SunCr' ; an EXCELLANT wealth of info; will investigate it on my next day off...Thanks again, and YES; it IS RHD converted (Obviously by a typical idiot)

:cheers:

 

:iagree: :cheers:

 

Important to remember that although the breakpoint is unknown, there are many late '85s that are the Aux Fan Switch in left head/Guage Sensor in right head configuration. Also the stock Aux Fan Switch close temp is around 240°F.

 

'89 per the Shop Manual is 226 main, 228 aux and I've verified that more times than I wish to admit with my scanner. 240 really seems high, you might want to swap it out for a lower temp.

 

If you just want to see if it will run or not, simply jumper the ALDL at A&B (top two terminals on the right) with a paper clip of short length of wire. The main fan should come on as soon as the key is turned to the "On" position, even with the engine not running.

 

Jake: You're right, but Smacko's fans appear to have been rewired so when he grounds the pins, the aux fan should come on. He'll need to ground the aux fan switch to turn on his main fan.

 

Thanks Sun & Jake but as SunCr's pointed out, it DOES seem mines been rewired using a diametrically opposed circuitry method (read also by a DUMMY!) hehehe, SO, with paperclip at the ready, which pins are the AUX fan jumpers (Which hopefully will bring on the MAIN fan)??

:hat

PS; I have done the above tests; removed high pressure switch AND jumped A+B on ADSL and BOTH tests DO make the Aux fan come on, but again - WHICH jumpers are SUPPOSED to make AUX fan come on, as they must be the ones I need to jump to have the primary fan come to life...


[Modified by smacko, 7:46 PM 9/22/2003]

 

Aux fan is controlled by the switch in the cylinder head, independent of the ECM so you can't jumper the diagnostic connector to make it run. Look between the #1 & #3 spark plugs (right side of the block closest to the radiator) or #6 & #8 (left side closest to the passenger compartment) for a green wire with an oval connector to the switch. Squeeze on the sides of the connector to release it (be careful, they're easy to break) and remove it. Ground the wire by touching it to the block with the ignition on. Fan should run.

 

As I said, thats what I did today (That AND short the 2 pins as per other posting) and BOTH methods made the AUX fan come on, NOT the main (primary) fan, which is what I want to make work...any ideas? :confused:

 

Up late - isn't it 1:00 AM, Tuesday, in Brisbane?

Sounds like only the pusher is wired up. Follow the harness from the main fan and see where it goes. On production Vettes, should be to a relay on the left fender well, near the battery which was on the left side. However, your battery is probably on the right side now and the Evaporator housing is poking out on the left, so you're going to have to follow the harness from the fan and see where it goes. The Relay for the Aux fan is on the left side of the radiator shroud. I would imagine that it's still there with the harness for the main fan spliced to it or, it's now the location for the relay that was the main fan with aux fan spliced into it. In fact, disconnect the main fan and jumper 12 volts to it just to make sure the motor isn't burned out. Each fan needs it's own Relay to handle the electrical draw. Otherwise you can burn up the Relay and once that happens, the fan isn't going to run, or it will run continously with the ignition off.

 

The '86 Electrical Supplement shows the same, but I've yet to encounter a stock Aux Fan Switch that closed before 235.

 

:confused:

 

Just see where the wires from the main fan go and post it - we'll figure things out from there.