Three fan relays off my 96 LT4 and on my 64 GS but I only need one. Anyone know how to tell the htree apart?

 

the 96 has a pretty cool setup. low and high speed, but both fans always run.

 

I will only have one fan and I have the harness just need to use the right relay

 

1 fan will always run in high speed.

 

????????

Not on a stock LT4......

Either both fans run or don't run.....when they are on they are either both running high speed or low speed.......that is both fans always run at the same speed...



Oh maybe you are saying one fan would have to run high speed since low speed is accomplished by running both fans in series so each fan sees only 6 volts and with one fan it would always have to see 12 volts??

 

I know how the LT4 fans work.....
if this guy does a custom application with 1 fan, it will only run in HIGH, 12 Volt mode. nothing else.

 

 

Thanks Larry so it really does not matter which relay I use?

 

You need to look at the schemetic, and choose 1.
you have to elimanate the series fan setup...

 

Two of the relays are four wire type, one is a five wire type. The five wire type has N.O. and N.C. contacts. The other two are just N.O.

If you just want to run the fans on high speed you might need to use both relays. One might not have sufficient current capability to run both.

Here's the schem for a 96...

This isn't going to be as simple as just rewiring things. The PCM controls the fans differently at different times depending on the circumstances.

 

My other option is to purchase a relay and wire it to an on off switch and not use the computer. Was trying to use one of the existing relays with the LT 4 harness. Thanks for your inputs

 

AllLT4 thanks for the pic as I mentioned I have two options, however there is only one fan, one connector and I do not think you want to run the relays in series so is there a final answer or should I just buy another fan relay and have an on/off switch. (this certainly is a run on sentence)

 

To use your own single fan to replace the factory dual fans and have the new fan run at full speed using the factory harness and assuming you're using the factory fuse block to supply the 12 volts for the fans and relays.

Use Fan Relay #1. You can identify Relay #1 because it will have the following wires at its socket.

Red wire 12 volts input for the secondary of the relay to drive the fan motor.

Pink is 12 volts for the primary relay coil.

Dark Green (Ground this wire, the relay will close and provide 12 volts to the fan via the Light Blue wire.

Light Blue wire. When relay closes 12 volts comes out of the relay on this wire which you wire to your Fan (Red wire).

Black wire of your Fan. (Run the black wire to ground).

If you reverse the polarity on the fan, the fan will spin in the wrong direction.

So in a nut shell you need to find the plug that went into the Left side factory fan. It will be a two wire plug with a Light Blue wire and a Black wire.

Cut the plug. You only need to use the Light Blue Wire.
Tape the end of the Black wire. (Won't be used)

Connect the Light Blue wire to your new fan's Red Wire. Run a wire to Ground from you New fans Black wire. To enable the relay you ground the Dark Green Wire either using the computer or manual switch.

You can leave all of the other wiring and relays in place.

 

Well said and well done

 

One more question which deals with your last paragraph "Connect the Light Blue wire to your new fan's Red Wire. Run a wire to Ground from you New fans Black wire. To enable the relay you ground the Dark Green Wire either using the computer or manual switch.

If I just ground the green wire as you stated before to I need to worry about the last sentence or do you mean I take that wire and hook it to a manual switch. I was planning on using the original fan harness but which is connected to a modified LT4 Engine harness? Did I loose you?

 

If you want to have the fan run all of the time, you can just Ground the Dark Green wire.

The fan wasn't designed to have a 100 percent duty cycle so I wouldn't run it that way.

You could use a manual toggle switch to ground the Dark Green wire so you can turn it on or off manually.

You could have a computer ground the Dark Green wire so when a certain temperature is reached the fan will turn on and off automatically.

You can also use a temperature switch that screws into the head (not sure about the LT4) so when the coolant in the head reaches a certain temp. the switch will short out and ground the Dark Green wire. It will turn off the fan when the temp. is below a certain temp.

In my statement about the Red and Black wires of your New fan, I'm guessing that's the colors of the wires. Red would represent positive and Black negative.

 

Thanks again, I will see if I can pick it up with the harness and computer. The harness was reworked and I have a OBD I PCM from PCM for less so I think thats the way to go. If not I will ground the green wire via a switch. Thanks for your help.

 

If you can find and post what year and model car the PCM came out of, some one can tell you what pin from the PCM to use to connect to the Dark Green wire.

Using the PCM to control the fan would be the best method.

 

Thanks