Question: How test cooling fan

[vdogamr]

My engine's cooling fans don't come on at all. There is a thread where someone posted a page of the Haynes manual on how to test the switch, relay, and fuse of an 84. I tried to follow it but ran into 2 problems.

1) How to properly ground the switch connector. I tried to ground what I thought was the switch. (It was between 2 cylinders and had only one wire running to it. ) Below it I saw a black wire bolted to the frame. I tried that. I also tried connecting my volt meter to the wire and to the neg battery terminal and got no reading. Yes the key was in the on position.

2) Where is the relay on an 88? There are several things in the location mentioned and none of them look like the image in the book. And does "jumping the relay" mean to close the circut with a copper wire?

Sorry if I sound like a total ameture (I am), but electrical testing scares me. I had a bad experience where a car I owned had the battery cables colored backward. Replacing the battery was... exciting. And I know shouldn't just go short circutting things to see what happens. I did take off the fan and hooked it up to some direct current and it turned.

Any help would be appreciated. I did order myself a copy of the Haynes manual. And I have the Chilton and owners' manuals.

 

[vdogamr]

So I have been learning a lot about the electrical system related to the fan switch and fan relays. And I want to see if I got it right.

The fan switch is a low amperage switch that when grounded causes current to flow through the coil side of the relay which magnetically closes the high amp circut to the fan.

So all I need to do now is determine which relay is the proper relay :confused and then close the circut of the larger connectors to see if it is the problem. And if I am right the switch wire does not need to be grounded because that only causes the relay circut to close (which I will be doing manually). I could also ground the negative side of the coil contacts to test the switch wire.

When doing this is there an electrical difference between the car being on and the key being in the on position? And does anyone know off the top of their heads which relay is the proper relay? (I narrowed it down to one of three :L )

 

[Toms007]

Wow, I can't help you, but lets keep this to the top so someone here, with the correct answer, will see it and post up. Where's geekinavette?

 

[geekinavette]

The fan switch is a low amperage switch that when grounded causes current to flow through the coil side of the relay which magnetically closes the high amp circut to the fan.

For systems that use a temperature switch directly...yes that is correct. In 88 I "think" there's one fan that works this way, and an auxiliary fan that the ECM controls? Not too sure there.

For the temperature switch controlled setup...the circuit diagram would look something like this:

Now this is a diagram for an '84 setup...I really don't know if any part of the '88 setup is the same or not. In this setup if you take the wire from either the temp switch or the AC switch and touch it directly to ground...with the ignition on...the fan should start. On the '84 the temp switch for the fan is the one on the passenger's side of the engine, between cylinders 6 and 8. There is another one that looks similar (usually has a different type of connector) on the driver's side between 1 and 3...that is for the temperature gauge. Again that's how the 84 is....no idea if 88 is the same.

For the system where the fan is computer controlled...the wire that goes to the temp switch/AC switch would go to the computer instead. The computer would have a circuit internally that would connect that wire to ground to energize the relay.

As to where that relay is located...all I know is where it is on the '84, and that is on the driver's side of the engine bay mounted to the fender well...kinda near the brake master cylinder...but the 84 only has one fan, I believe in 88 they had two?

 

[vdogamr]

Thanks a lot

Thanks for that diagram. That is very helpful. On my 88 I have traced some wires and found the the relay is on top of the fan (kind of driver side). I removed it, and using a volt meter tested it. It didn't work so I took it apart . Turns out the magnet coil is shorted and does not make a magnetic field.

I don't know how, or if, the AC is combined into this circut. With the way my new car is, I assume the AC is also broken.:L

I am pretty sure buying a new relay will fix that fan, but I don't think it controls the aux fan. Like you said, I think it is controlled by the ECM, but I have no idea under what conditions it turns on. I wonder if it has another broken relay.

 

[muddywaters]

I noticed on my 88 coupe, when I pulled the codes using the paper clip trick, both my fans came on.

 

[vdogamr]

OH CRAP!

What did I do!? hnoes

So I bought a new relay and installed it. Then I went to back the car out of the garage, and I noticed my LCD wasn't lit. At first I thought it wasn't on and that maybe I had not properly put back a fuse. Then I looked closer, and noticed that all the individual LCD lights were comming on and going off (very dimmly) in a wavy pattern.

How could I have screwed up the LCD? Is it safe to drive it to a proper mechanic?

 

[geekinavette]

What did I do!? hnoes

So I bought a new relay and installed it. Then I went to back the car out of the garage, and I noticed my LCD wasn't lit. At first I thought it wasn't on and that maybe I had not properly put back a fuse. Then I looked closer, and noticed that all the individual LCD lights were comming on and going off (very dimmly) in a wavy pattern.

How could I have screwed up the LCD? Is it safe to drive it to a proper mechanic?

That's what it'll do if the cluster isn't getting any power (like if you pulled the LCD fuse). I don't think it'll "hurt" anything to drive it somewhere like that...I've done it several times!

 

[vdogamr]

If nothing else, thank you for alleviating my fear enough that I can stop worring about it while at work.

Much calmer now . Thank you

 

[vetteoz]

In 88 I "think" there's one fan that works this way, and an auxiliary fan that the ECM controls? Not too sure there.

Other way around
ECM controls main fan and temp switch in Drv side head controls Aux fan IF fitted.
Can check Aux fan operation by pulling wire off switch and grounding it.
To the OP.
I am unsure what relay you replaced.
On my '87 and '89 cars all the relays (fans , fuel pump , TCC ) are by the firewall;on the '90 + cars ,the fan relays are on the radiator shroud by the Drv side headlight.
I have never seen a C4 with a relay on top of the fan; possibly aftermarket

 

[geekinavette]

Other way around
ECM controls main fan and temp switch in Drv side head controls Aux fan IF fitted.

I knew it was something like that!

So where is the gauge sending unit?

 

[vdogamr]

Because this problem has stopping being about my fans and moved on to "OMG my car!", I started a new thread about the display.
Swapping relay messed up LCD display

Not that I don't want to fix the overheating problem, but it isn't going to overheat just sitting in the garage.

That's what it'll do if the cluster isn't getting any power (like if you pulled the LCD fuse). I don't think it'll "hurt" anything to drive it somewhere like that...I've done it several times!

I checked the fuses. (anything that even sounded like it could be involved) They look fine. I wish I could show you what the display does on start up. It does not look normal, or out of power. (Except the backlights, they look out of power )

 

[vetteoz]

So where is the gauge sending unit?

Pass side head between # 6 and 8 plugs.

Fan control varies by year.
As I recall.
'84 has temp switch for fan only ,no ECM control;
'85 has ECM control but temp switch acts as over ride backup direct to fan
'86- '89 as stated above
'90 onward ; both fans on ECM ; no temp switch.
And all have provision to turn the fans on with A/c on.

 

[vdogamr]

Is that this

Is that what this is?

This is what I mistook for the fan switch. You will notice in the picture that there is no longer a plastic cover on the wire. It was so brittle that it broke in my fingers.

This green wire (again I was stupid) is what I tried grounding to get the cooling fan working. Could I have done something bad? Or maybe is there a connection I could have ruined near here?

 

[vetteoz]

That is the sender unit for the dash temp gauge , direct short may have done something to ECM but should have only made temp gauge go fully one way or other.

IF you have 2 fans ,the Aux fan switch is on the other side between # 1 and 3 plugs

 

[vdogamr]

Yes, finding the actuall switch for the aux fan made me realize that wasn't it.

However since my car got up to 250, I assume neither fan was working.

 

[vdogamr]

So since I am still working on the LCD issue, while I had the hood up I decided to ground the correct wire. So I unplugged the temp switch and turned the key to on and then grounded the wire that was connected to the switch. I decided to do this using my voltmeter and I read about 2 volts. Is that right? The fans didn't switch on, unless the aux fan is so quite that I need someone looking at it.

What are the symptoms of needing a new ECM? I am still not sure it isn't a relay or wire, but everyday I think I may have screwed up something important. And one more question, what conditions make the ECM turn on the main fan?