Here is the problem: My main cooling fan comes ON a second after the car is started cold. Basically it runs all the time regardless of temp. With the key in "ON" and the engine off it does not run. Seems like I have the opposite problem than what most C4 owners experience. Any tips on getting it to work right?

 

Hi

Check your a/c fan request pressure switch, there are two close together. the high press switch has two spade terminals, beside that is the fan request switch (has a small round connector) if that is unplugged it can run the fan whenever the ignition is on.

Have a look at the wiring diagram below to fault find.

Either the a/c fan request switch is faulty, ecm fault or if your car has only the single fan (no booster fan in front of a/c condenser the temp switch in the head can run the main cooling fan. on the booster fan type that temp switch runs only the booster fan.
The ecm grounds the fan relay (or in single fan the override switch in the head).

Dual fan diagram.



Single fan diagram. The fan override switch is in the head (Passenger side on some) has a single wire with a round connector.

 

I am pretty sure I have the two fan system, one puller fan on the back of the rad, and a smaller pusher fan on the front side of the ac condenser. Ill check again tonight

 

Also check the fan relay which is on the drivers side wheel house, often times people ground the green wire to keep the fan running. Not a good idea.

 

Very possible someone did that.

 

That can't be the case here. If that were true, the fan would run as soon as the key is turned on. ChsTitans has said the fan doesn't run until he starts the engine.

My question for ChsTitans: Is your a/c control ON before you start the engine?

 

or on defrost

 

I did have the brains to check the A/C. It is on the heater mode, and the ac clutch is not energized so I am pretty sure the A/C is not on.

Am I correct in assuming that the little fan in front of the condenser is just like an emergency fan, NOT an A/C fan? I assumed that was for extra cooling when the A/C is turned on, but I guess the A/C when on will trigger the main fan. Learn something everyday.

Either way, I have the main fan running at all times.

 

If you have the two fan system, the first schematic tells us the front fan is controlled only by the coolant temp switch, not the ECM.

Is this new information? I thought you said that the main fan runs after the engine starts, not at "all times".

I'd suspect a bad High Pressure Switch in the a/c compressor. You'll need to put a jumper across that switch to simulate a "closed" switch. When this switch "opens", it tells the ECM the a/c pressure is high, which turns on the main fan.

 

Sorry I meant that the fan runs when the engine is running only. I will be checking that ac switch tomorrow and update you guys. I have a feeling it is that or it is the dash controls

 

Nothing wrong w/ main cooling fan running all the time.

 

Why shouldn't a nice Corvette work the way it is supposed to?

If it ain't broke, you haven't worked on it yet?

 

Wrong. These electrical fans were never designed to run constantly as were the old style fan belt driven fans on older cars. Yes, you can set up the electrical fan to run constantly, but the life span of the fan motor is decreased severely and may burn out on you at the worst possible time.

 

You got proof.Ive got an electric fan running constant on my truck for 6 yrs now AND its my work truck driven daily.

 

hi titans. i have an 85 (currently doing its head gaskets and trying to fix a crap idle) and i had the same issue as you.

here is the sensor that was acting up for me. when i jiggled this sensor, the plug, it would activate the fan. sometimes when i started the car it would be on, sometimes not.

it was cliff harris in another thread whi drew my attention to it. i spread the plug pins a bit to make sure there was better contact in the plug. my sensor was good but because the "open" ground position turns the fan on, when my plug pins lost contact, the ecu saw "open" on that circut and on went the fan. when it was cold on startup it would happen alot. then as the engine bay warmed up the pins contacted the switches plug which was off because i didnt have defrost or ac on...the fan would turn off.

i also put some dielectric grease, silicon grease, on my ug connection.

hooefully that is your issue. you can test it easilh enough.


careful with the plugs release. the old plastic is brittle. also it will only go back in one way, line up the slots.

cheers and hope this easily fixes your issue.

note that its possible the pressure switch itself has failed in the open losition. my guess is you could ground the plug and shut the fan off. then if you unfround the ug it starts again that would imy its related to the ac switch. if you ever so slightly bend the tabs a bit (like...barely...just to make contact) and the fan still remains on, then its probably the switch that is stuck open, not a faulty connection from the switch to the harness.

also note, im not an expert by any means on this electrical stuff, so look for the troubleshoot orocedure with the ac pressure switch elsewhere to make sure what i have said is correct. i can verify its what worked for me but im not an expert.

(for example, i never "closed" the circut back to the ecu when the plug was unplugged.....but that theory of narrowing it down mighg work).

sorry to be wishy washy.

VikingTrad3r







passenger side, for orientation, thats the dipstick tube, sans the dipstick, to the left of the exhaust manifold flange on the y pipe.

 

VikingTrad3r thanks so much for the info and pic! Before I look into anything else, I will look into this. Fingers crossed that it is really that easy! The interesting thing is I am pretty sure that the fan was not running all the time when I bought the car and drove I home. We will see!

 

Good for you.