cooling fan woes, can't figure it out (long)

[nuc]

This started some time ago, I got annoyed at the car and haven't touched it for awhile. I took a look at it again today and am still stumped. A couple months ago the cooling fan stopped turning on when the car heated up. If I didn't turn the A/C on (which did turn on the fan) the car would overheat. The relay which controls the speed of the fan has long been removed and it always runs on high when it does run. I replaced the fan switch that screws into the manifold with an ac/delco replacement thinking that that was the problem. Doesn't help. I switched out the relays on the drivers side engine compartment. I can feel them click when the A/C turns the fan on, so they do work. Didn't help the problem. When I ground the wire to the metal side of the coolant switch the fan turns on ok. So the switch is grounding through its threads to the manifold. I tried using a piece of wire from the sensor wire to the sensor electrode thinking maybe the sensor connector was not making contact with the sensor electrode. Didn't help. I am out of ideas. Does anyone have anything else to try? Could I have gotten a bad replacement coolant sensor from the local buick dealer? Thanks

 

[::2dFx::]

Not likely, have you tried actually replacing the relay? True it may work, but there may be fault in another part of the relay.

 

[rob nolan]

Mine is doing the samething i got a new relay on the way. So i'm gonna try that first.

 

[salvageV6]

Clicking and WORKING are two very different things.

A click means the solenoid action is pulling in the contacts but if they are melted or used up down to nothing or burnt up they will not flow enough current to turn on the fan.

I was able to clean some up with a small fine file but that involved opening up the relay and working on it.

I'd try a new low speed fan relay.

Low speed is commanded by the computer not a sensor.

I don't know why anyone would mess with the chip low speed wiring other than using a simple jumper to make it run on high speed when any fan turn on is commanded.

You are correct that the temp. sensor should command high speed fan operation just like with the A/C on.

But that sensor is over 220*F before it kicks on.

I would be more worried about the 160* ECM commanded fan wiring and relay.

Then fix the high temp. fan switch (sensor).

 

[nuc]

Is there a way to check to see if the computer is maybe not commanding the fan to turn on? I am running a computer that has been modded for low impedence injectors. I will take the relays and buy 2 new ones.