steven mack

I am trying to find a reason my main fan comes on when I start my vette.I did the tests in the factory manual and still can't figure it out.If I turn the key to the on position, motor not running ,and disconnect the wire from the the temp sensor and ground it the fan will not come on.if I turn the motor on the fan will turn on.If I disconnect the relay it will turn off.I have checked the wire from the harness and it's not grounded anywhere.If I do the same test on the auxiliary motor it works properly.One more thing the fan will sometimes shut off for a moment then come back on even though the motor is cold and just started.

rodj

What sensor ?
Main fan is controlled by the computer ; not a temp sensor

Only the Aux fan ( if fitted ) has a seperate temp switch

Is the plug on the A/c line pressure sensor correctly

rob-cyn

mine runs all the time too

1986coupe

Are you getting any codes? The fan can sometimes run when something that seems unrelated is having a problem, such as the ignition module (that happened on my friends 94)

anciano

Switch relays from one side to another. If the other fan then comes on, you'll know it's a bad relay. If the same fan comes on, the problem is somewhere else.

AGENT 86

There are a few things that will cause main fan to run, grounding the gauge sender is not one of them.

Limp home mode, is the SES light on ?
AC, Is climate control on defrost ?
Is A and B jumped at ALDL connector ?
Is there a short to ground on circuit 335 ?

steven mack

None of those things are happening Agent 86.I did try and switch the relays no change.Sometimes when I start the motor the fan won't come on at first for a few minutes then it will come on then go off and then come on again before it gets up to temp.Very strange.Thanks for the suggestions guys I will keep looking for a solution.

sailorsteve

Section 8A in the FSM describes how each circuit is supposed to work, as well as the diagnostic info. Did you determine that your fan is in fact not behaving?

FLASH92LT1

Do you have a performance chip in it?

My '92 has a FastChip in it that turns both fans on immediately. I don't know why.

Rick - '92 LT1 - in Memory of Dad

steven mack

I never looked to see if the computer had an other than factory chip.The previous owner never mentioned it.He was pretty specific on the changes to the Vette.He gave me all the receipts he had.

steven mack

Sailorsteve I have read and reread the factory manual.I did the tests in the manual still can't find if it is working right.My 85 and 86 did not work like this maybe 88 is different?

engle1147

There could be an issue with the coolant temp sensor (the one on the front of the intake - not the one in the head that the cluster gauge uses) the computer uses to trigger the the main fan relay.

steven mack

I haven't checked that one but I will.Thanks Engle

Corvette0096

Steve let us know.

steven mack

Corvette0096 I was going through the folder of parts and repairs that I got with the Vette.I found a print out dealing with a fan conversion kit.I do not have a receipt for the kit .The Vette came from Texas where it gets pretty hot so the previous owner could have changed the way the fans operate.He also put in a high flow water pump and Robert shaw thermostat.All the fan wiring looks stock so I'm still perplexed.

sailorsteve

Maybe you can get some info from the previous owner.

AGENT 86

Any unknown switches anywhere ?

jeffp1167

My 90 does this periodically when I disconnect the battery cables. When I reattach the cables the climate control switches to auto when the key is turned on and the fans run.

steven mack

Hi Jeff I noticed that about the climate control turning on when battery is reconnected.I made sure it was in the off position.Thanks for the input.

REDC4CORVETTE

Is your A/C plug connected?