I have an 87 Iroc, engine intake all been changed prior to my ownership to a 327 block and 305/350 intake and heads. It is now a carb engine.
My coolant fan runs all the time from the time key is turned on from when shut off. I have spent hours searching wires. I have 2 fans one for the a/c and one for the coolant. I want to install a sensor for the coolant fan to cycle on. My problem is every diagram i have looked at does not show which wires or where the fan realy gets its power from other than the EMC. The other thing is the fan for the A/C what triggers that to come on, is it the high pressure switch? I thought it was wired to come on when A/C was turned on.

 

As I understand it on a dual fan setup - the ECM gets a temp reading, and signals the fan relay to turn on/off the primary fan. Secondary fan is turned on/off with the A/C switch as mentioned.

If your wirings been hacked beyond recognition, you might consider a seperate fan controller and wire it in place of the factory stuff. There are many, I have a Flex-a-lite that I'm extremely pleased with - they make them available for dual fans, they connect in with the A/C wiring to run the secondary fan, are fully temp adjustable on the primary fan, and most have provisions for a toggle to manually run fan as well. They get their temp info from a probe that slips inbetween the radiator fins. Best of all, they come with their own wiring so no need to track down any factory wiring (except wires to fan)and it's a simple install. Check them out at Summit or Jegs.

 

Thanks so i understand, the ECM gets signal from from temp reading for cooling side? Do you know is the sensor the ECM gets its reading from 1 drk green wire? I have been going crazy trying to figure this out. So much so i went to the GM dealer today and talked to one of the parts guys. He said the same thing you are saying what he said in addition to that is there is a button type sensor that closes a circuit to start the fan. From what i am getting from all of this is that sensor/ button switch triggers a signal to the ECM which in turn starts the fan?

I was going to try the type you are talking about an adjustable thermostat, probe goes in the radiator where though? Mid top or bottom? Do the instructions tell you were to put the probe? I really REALLY wanted to keep this as original as possible, but i may have to modify it.
I also planned on putting a switch underneath near the steering column so if temp went to high i could turn the switch on to start the fan.
This is driving me crazy.
Thanks for the help, i see i am not alone in dealing with this problem.

 

This is what I am going to try this weekend when I can get to the JY to get a connector. I will be posting my result in this thread after that.

https://www.thirdgen.org/forums/elec...ng-please.html

 

Hey king, it worked. I had to buy a thermal switch and connector for it and mount it in the head. Using the existing fan relay, the black/pink goes to the fan positive. The fan negative grounds to the body. The orange goes to a fused battery source. The whitish, beige goes to an ignition source, and the green/white goes to the thermal switch.