GTAlover

I have a 1986 TPI 305 with the factory single fan setup. I just purchased a Hypertech Fan Switch from Summit. I now know that it won't work due to the ECM controls my single fan. My question is can I install this fan switch in my head and wire it up to my fan to turn it on through the Hypertech fan switch??? If not I'll buy an adjustable one and go that route.

safemode

iTrader: (1)

I thought the fan is controlled by mechanical switches to relays, with no ecm handling at all. I'm pretty sure that's how it's done anyway. I have the wiring diagrams in the shop manual at home, and i dont remember any of it being routed to the computer. ... though i have a 92 tbi

GTAlover

On my car the ECM controlls the fan.

Anyone know if my idea would work?

83Firebird420

yeah ecm controlls it...if u know someone who burns proms they can change it.
the sensor is reading resistance through the temperature of coolant. and when the temp gets hotter the sensor tells the ecm its getting mor or less voltage (cant remember) and turns the fan on. so im not sure if ur idea will work...but i could be wrong...

GTAlover

I looked at the wiring diagram at both my 86 TPI with single fan and a 88 TPI with dual fans and I wonder if on my car car if I could take the dark green/white wire that is going to my ECM from the coolant fan relay and route it to my fan switch if that would work. It looks like that is how gm has it setup for that second fan that is controlled by the fan switch on the dual fan setup. Could someone with some electrical knowledge take a look at this for me and see what they think. I got the wiring diagram from

http://www.autozone.com/az/cds/en_us...rInfoPages.htm

Also is there just one wire that goes to the fan switch?

GTAlover

I think I got it figured out. I found the coolant fan relay (sort of by the passenger headlight) and found all 4 of the wires: dark green/white, brown, orange, and black/red. The dark green/white wire goes to the ECM and this wire turns the fan on when it reaches whatever temp the ECM is set at to turn the fan on. All this dark green/white wire does is when it gets grounded it turns the fan on.

The fan switch that is located on the passenger side head that is found on dual fan setups (and SOME single electric fan setups) grounds this wire on the secondary fan (and some single fans) to turn that secondary fan on whenever the fan switch grounds itself by whatever your fan switch limits are.

I tapped into the dark green/white wire by the relay and grounded it and sure enough the fan turned on. So all I need to do is install on my new Hypertech fan switch in the head where it's supposed to go and run that tapped wire to my newly installed fan switch. This should turn my single fan on at 176 and shut off at 160 and if the fan switch should ever fail the computer will still be able to turn the fan on at the factory setting. So if anybody has ever bought the Hypertech Fan Switch from Summit thinking it would work on their 86 TPI (Summit does have it listed for 86 models but doesn't specify it won't work on the TPI) can still install it and make it work.

83Firebird420

but would the fan always be on as it will think its grounded through the switch?
i think to do what u want to do, u will need an adjustable fan switch with the probe that goes into the rad fins.

GTAlover

Yeah it gets grounded through the switch, but the switch doesn't ground itself until it reaches 176 and then ungrouds itself at 160. That's all that switch is designed to do.

86firebird350

ive got a hypertech fan switch on my 91 L03 with a single fan and it does not turn the fan on at the set temperature. is this because the ECM controls the fan, even on single fan setups, and is not set to turn on until a higher temp? because i always thought that the single fan setups were controlled only by the fan switch in the head. and in dual fan applications, the fan switch controls the secondary fan. am i wrong?

GTAlover

On the TPI with the factory single fan setup it is controlled by the computer only. I dont have any wiring for a fan switch at all or a fan switch from the factory for that matter.

I think on your car your fan is controlled by a fan switch even though it's a single fan. Check out the wiring diagram for your car and you should see that the fan control relay is controlled through the fan switch. You might have something wrong with your fan switch if it doesn't kick on when it's supposed to. I guess they are prone to getting out of calibration due to being so close to the manifolds.

http://www.autozone.com/az/cds/en_us...rInfoPages.htm

You're right the dual fan setups had the secondary fan kick on through the fan switch and the primary fan turned on by the ECM.

smallblock383

or...another possible quick fix, which doesn't effect the ecm, relays or anything else. Take the wire that went to the fan switch on the head, add to it, I used a soddering iron and silver sodder. Run it through the firewall, over to the drivers side, and in a good easy access spot mount a two wire toggle switch. Hook the wire on it that you pulled through, and then another piece to a any screw to ground the switch....BINGO manual fan switch, problem solved!

GTAlover

I would still have to have the spliced wire coming off the relay because there is no wiring at all from the factory for my fan switch, hence my problem. If I didn't do it like this then I would have to wire up some new wires that go to my fan in order to turn it on.