dual fan switch
 

I don't have my manual here but need to learn about the fan switch in my 89 formula with dual fan set up. Anyone have any literature?

How would I ground it to test my fans? After it's grounded will one or both fans spin? I suspect the switch may be issue with why my Fans aren't coming on and any help is greatly appreciated bc i can't drive my car until I sort this out...

Re: dual fan switch
 

Does at least one fan spin when you jump the ALDL connector?
That one comes on when the ECM reads a certain temperature from the coolant sensor up front and sends a signal to a relay.
The other fan only comes on when the pressure switch in the passenger cylinder head closes.
When that switch closes, it closes to ground, so I guess if you pull the plug off the switch and ground the plug, your fan would come on.
Don't know how you can ground the switch itself, being pressure based.

Re: dual fan switch
 

google "austin third gen wiring" this has wiring schematics for 82-92 engine and body wiring. Or try this link http://www.austinthirdgen.org/?pid=19. one of them should get you there.

Re: dual fan switch
 

Thanks NCC. my first fan comes on only for a few seconds but my temp gun reads 245. what would cause the fan not to run if the temp is high enough?

what causes the second fan to engage? Pressure from the AC? I tried running my AC but it didn't engage the second fan

Re: dual fan switch
 

I guess your engine needs a certain temperature before the addition of the A/C can creat sufficient pressure for the switch to close.
Without adding the A/C engne temp needs to be even higher to create the pressure.
As far as I know, this is it. I've never seen my secondary fan run, either.
Never got to such high temps.

Re: dual fan switch
 

Take the wire off the switch in the passenger side head and ground it to chassis ground. With the ignition in the "run" position but car off, the second fan should engage. This simulates the fan switch closing.

Do the fans turn on with the AC turned on? If they do, then you know the overall circuit is good. If they don't, you have a wiring issue somewhere.

On yours, the primary fan comes on with an ECM command, the second fan is temp switch controlled. I don't know how to "simulate" the ground on the primary fan on those.

Re: dual fan switch
 

To answer your question ozz1967 if a 88-92 ECM is disconnected grounding the iirc green/white wire is grounded to command on the primary fan. Or jumping the aldl a to b the fans will be commanded on.

Re: dual fan switch
 

Hi, I wanted to ask: So one would need to disconnect ECM to do this test?

Re: dual fan switch
 

That's what I posted above !

Re: dual fan switch
 

This is c1 on the 165 ECM green/wht wire. E8 on a 730 ECM .

Re: dual fan switch
 

Ok heres what i found and believe to be true but please verify!

The primary is controlled by a temp switch in the block between 6 and 8 spark plug. It grounds the relay and triggers the fan at a certain temp.

Where it gets confusing is with the secondary fan. It seems in the manual they reference a "auxiliary coolant fan switch" and a "fan pressure switch". Both are involved somehow in engaging the secondary fan. It's around page 1310 in the 88 service manual I don't have it in front of me. Does the secondary really use both?

Re: dual fan switch
 

I know One fan is controlled by the A/C, when it is turned on, I believe it should turn on. The other is controlled by the Temperature switch on the side of the block. I do want to think that there is a control in the ECM for one of the fans as well... not sure if it is the AC fan or the other fan...

I have often considered wiring them up to a switch on the dash so I could turn it on when it got warm...

Re: dual fan switch
 

I see many great Tech Articles under Common Cooling Questions at the home page of Tech/Cooling Forum.

https://www.thirdgen.org/forums/cool...ions-read.html

Re: dual fan switch
 

Thanks but I didn't see anything really on the AC pressure switch did u?

I am reluctant to use a switch because I don't want to worry about flipping them on/off and want to keep it stock as possible. I guess my question is does anyone have a pic of the AC pressure switch? Manual shows it in passenger wheel well

Re: dual fan switch
 

It's on the hard line about 2-3 feet back from the condenser before the receiver dryer.

Re: dual fan switch
 

What is funny, is my 87 (when it was an LG4) the fan was attached to the AC Switch itself on the dash.... My Freon was low, and my car was hot, so I turned on the AC to turn on the fan... When I converted to Dual Fan 87 TPI, it moved to the switch on the AC unit by the dryer. So the pesky little fan would not turn on if I did not have freon... (which makes no sense to me)

Re: dual fan switch
 

I have the same issue...my AC blows warm so no freon. My secondary fan will not kick on either. Maybe after I charge it?

Re: dual fan switch
 

I would think it would greatly increase the likelihood. I know with low Freon, my one fan will not turn on at all, How I believe it works (might be wrong) is there is a signal it sends to the ECM, and the ECM can turn on the fan for high temp, or AC pressure, or other reason (that I do not know of). The second fan is controlled solely by the switch on the side of the block.

There are relays for each fan on the Passenger side front, by your Air filter area, I have had those go bad...

Re: dual fan switch
 

I finally got out here and for some reason as soon as I fired up the car for the first time the auxiliary fan was spinning from the start. I even unplugged the secondary fan relay but it kept running, how could this happen?

Re: dual fan switch
 

I suspect either you disconnected the wrong relay or it is wired incorrectly.

Either way it should not come on when it is cold

Sounds like someone wired it directly to the accessory to turn on whenever the car was running... Does it turn on when in Accessory, or when the engine is not running but the key is in run?

It should also do this if you jump the ALDL, I also believe it could do this if you have a bad ECM

John

Re: dual fan switch
 

i actually found the issue over the weekend and it was what you said initially. underneath some black electrical tape on the wires before aux relay, someone crossed the power and ground wire which was causing the circuit to stay grounded permanently. this explains why even unplugging the relay didn't stop the fan from spinning.

i also replaced my CTS even though the one i installed last summer has less than 500 miles on it, and now my primary fan works. i measured the temp with a heat gun and the primary kicked on around 235 and shut off around 220.

what's funny is that when the secondary was rigged to run constantly the primary never had to engage because the car ran much cooler around 195. i may actually put it back as i prefer the car to run cooler, contrary to GM designing these cars to run hot for the sake of emissions.

thanks everyone for the help and hopefully someone else can use this to solve their fan problems
https://cimg7.ibsrv.net/gimg/www.thi...c3f2114c23.jpg

Re: dual fan switch
 

Thank you very much for posting this picture. I combined the two wires and my fan is now on full time,the over heating problem is fixed until I can get a switch wired in.

Re: dual fan switch
 

I understood that the switch on the side of the block would kick the fans on at 238F or if you turned the ac on?. Could you replace this switch with a lower temp one so the fan came on sooner? I have removed my ac system and converted it to a 1LE delete setup. Just wondering. Someone currently has the block switch plug grounded so the fan comes on when the key is turned. Trying to put it back working the way it should.

Re: dual fan switch
 

On a single fan system, the switch in the side o the head turns the fans on at 225* or so. This switch is completely separate from the AC set up. AC will turn things on regardless of the temp o the switch you have.
If you put a lower temp switch in, the fans will turn on at a lower temp. I currently have a 205* switch in my 84.

Re: dual fan switch
 

mine is the dual fan with one fan being controlled by the ecm, the block switch turns on the secondary fan I believe.