djmarch

iTrader: (4)

My left, (driver's side), fan turns on as soon as I turn the ignition key to the on position. Did some quick troubleshooting by diconnecting the temp sensor below the thermostat first, still came on. Replaced the fan relay with a new ac delco, but it didn't solve the problem. Anybody experience the same ? Any recommendations will be appreciared...

Thanks

cdoyle

That's the high temp fan right? Mine was doing this, it was always on.
There is a sensor on the passenger side of the engine, you have to get under the car to see it. I replaced that, and everything started working again. Just be aware once you remove it, all the coolant comes out. I found that out the hard way lol.

m smith

If the coolant temp sensor fails the primary fan will come on so unplugging may not show anything.It is possible that the sensor has shifted out of calibration telling the the computer it`s over 106 celsius when it isn`t.Also check the green/white wire for the primary fan because if it is grounding out somewhere the fan will come on with the key on.You replaced the relay but there are two relays,one for primary fan one for secondary fan.Primary one is on passenger side rad support secondary is on passenger fender by the battery unless someone switched them.Don`t know which one you replaced.

djmarch

iTrader: (4)

Thanks for the info guys..So the primary fan is the one on the driver's, (left), side ?
The relay I replaced was the one mounted next to the radiator on the passenger side. The relay mounted to the inner passenger fender next to the fuel canister is for the secondary fan. Is this true ? Correct me if I'm wrong, but a source explained the fan circuit to me is that the driver's side fan is the primary and is controlled by the temp sensor located on the intake just below the thermostat. And turns on around 200/210, give or take a few degrees. (via the 195 thermostat). The passenger side fan, (secondary), is controlled by the temp sensor located below the passenger side head and turns the fan on around 220/230 give or take a few. All controlled by signals from the ECM. I understand turning the AC on will turn the secondary fan on as well. Is this correct ?
I will check the green/white wire for any damage.

Thanks again..

m smith

The primary fan(drivers side) is controlled by the ECM to come on when the coolant temp sensor sends a signal to the computer indicating a temp of 223 degrees F (106 C) or higher.The secondary fan is controlled by the fan switch between #6 and # 8 spark plugs and is NOT controlled by the computer.The secondary fan will turn on with the A/C on if there is enough pressure(233psi) to activate the pressure switch in the A/C line.It will also come on if the temp reaches 238 F. The temps mentioned are factory stock settings.

djmarch

iTrader: (4)

OK...So I can rule out the temp sensor below the #6 and 8 spark plug as the reason my primary fan turns on when I turn the ignition to the on position...

Thanks

m smith

You`re welcome.Don`t know if you are the first owner of the car or not but it is possible someone rigged the fan to purposely come on when the car is turned on.That would be done by purposely grounding the green/white wire from the primary relay.This may sound stupid but did someone accidently leave a paper clip in the ALDL.That would also make the primary fan come.

1990 Nightmare

I have close to same problem but passenger side fan comes on and car wont start

djmarch

iTrader: (4)

No...This is an issue that just started last week for unknown reasons. Had done no work under the hood prior to this.

m smith

1990 Nightmare try removing the fan fuse from the fuse block.If the fan keeps running try replacing the relay.If the fan stops put the fuse back in and remove the wire to the fan switch between #6 and#8 spark plugs.If the fan goes off then the switch is stuck closed and you need a new one.If it still runs then the fan switch wire is grounding out somewhere between the fan switch and relay.Hope this helps.

Tibo

iTrader: (15)

Take a look at this:
http://austinthirdgen.org/mkportal/m...ine_wiring.gif

djmarch

iTrader: (4)

Thanks a bunch

djmarch

iTrader: (4)

Update...Came to realize after a closer look that it's both fans that are turning on when ignition is turned to the on position..

Tibo

iTrader: (15)

They might share either the same ground wire or the same output power wire.

chevypower91

Hi there, do you have headers? If you do, you may have some wires related to the fans that have burned touching the headers. This happened to me a few years ago.