Okay, which fan goes to what? I always thought that the big black fan that was behind the radiator was the main fan, now I am told that a smaller fan that is in front of the radiator that can only be seen if you lay on the ground in front the car, is the main one. Which is which?

My problem is I just went through quite a bit of work to convert to r134 to get my AC going, took a lot of work and replacing parts but it does work now. Problem is, neither of my fans kick on at all and I overheated the other day.

Even before working on the AC, the only fan that kicked on was the large plastic black fan behind the radiator. When the temp hit 235 it would kick on and bring it down. Now nothing kicks on. I don't think the other fan ever came on. Has this been wired up different? Is the wrong fan doing all the work (or was doing all the work before it quit working). Anyone with fan experience please let me know what process I need to take to figure out what is what and what should or shouldn't be turning on.

These cars always run hotter than they should, but this car has never overheated. The hottest it ever got was 245, and that was sitting in traffic for a long time. When I am moving the fan never kicked on because it always ran 190 or less (usually 160 when it is cool outside).

I am hoping this is just a relay issue. Checked all my fuses and everything is good in the box but I know there are inline fuses under the dash, which I hope I don't have to fish out.

The great thing is I finally fixed the AC and it is supposed to get up to 100 this week... Now I can't even use it and probably won't be able to drive the car, which is a daily driver. This car has been an electrical nightmare, every time I fix one thing something else goes out.

 

A/C operations when the a/c is turned on the big fan by the belts should kick on soon there after. Question when converting the a/c did you do anything with the a/c pressure switch.

the smaller fan is what I used to call a mayday fan it only would kick on if meltdown was imminent

if you go to your ALDL connection (little black plug under dash CAR NOT RUNNING ignition on)and jump A to B the fans should kick on, that will show that your fan system does work. and now you just have to find what sensor is not sending a command. if memory servers me there are fusible links for the fans by the brake booster behind the battery I am doing this by memory and its been 20+years since I had to chase such a problem, and while your in that area by the Battery there should be a few relays there give them a little tap with a screw driver one of those is a fan relay the other is a fuel relay and if a manual shift there may also a Overdrive relay and they look a like because I think they are.

1) with A to B jumped do fans run? 2)do I have power to the big fan using a test light or a DMM. if yes have power, bad fan or ground

remember check grounds always

 

Will have to check that tomorrow. So, when your car hits 235 which fan is supposed to kick on? Right now nothing is coming on, but in the past the fan by the belts was turning on.

 

Hi

This wiring diagram may help you.
The ECM turns the main cooling fan on when the temperature reaches around 225F or the a/c is on and the a/c pressure switch is requesting the ecm to run the fan. (removing the small round plug on the small liquid pipe will turn the main cooling fan on) The booster fan is an option and that turns on via a temp switch in the cylinder head at around 238F.

Your C4 is maintaining 230F for emissions purposes, you can easilly add a thermo switch to turn the main fan on earlier just connect one ground wire to the t/stat and the other to the green/white wire. Or get the ecm chip changed to run cooler.

One of the biggest problems is the C4 is a vacuum cleaner on the highways, all the leaves and twigs end up between the radiator and condenser blocking the radiator.

 

The auxiliary fan (the one in the front) will NOT turn on if you jump A & B on the ALDL connector. The only thing that turns on that fan is the thermal switch in the head. I believe it is on the passenger side in '84 and '85. My '86 has it on the driver's side and I believe that is true for all later years. You can turn on the auxiliary fan by removing the connector from the thermal switch and jumping the connector to ground. That should turn on the auxiliary fan relay and the fan.

The fan behind the radiator is operated by the ECM in '85 and later cars. The ECM decides when to turn on the fan (228°) based on the temperature it sees from the CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body. The ECM should also turn on the fan if the AC pressure switch senses that the AC is running. This is a normally closed switch that goes open when the AC is running. You can simulate this by removing the connector from the switch, in which case the fan should run.

 

cliff, my 85 is in the paint shop so I can't check, but pretty sure both fans came on when I jumped a and b on the aldl...been awhile since I did it....

 

Only the main fan comes on when ALDL is jumped A_B on the 85 vette. The auxiliary fan gets its signal from the sensor located between spark plugs 6 & 8.

 

thanks, you're probably right...had it on a manual switch for a long time now so haven't paid attention.

 

thanks, you're probably right...had it on a manual switch for a long time now so haven't paid attention. now that i'm typing this I remember posting a thread because it didn't come on with a/b....put it on a manual switch....getting old is hell....