Lesrace82

iTrader: (8)

There are Three relays for the cooling fans. Two wires from the PCM control the three relays. At what times do the two wires actuate the relays? Does only one fan come on at normal operating speeds? And then both fans come on when it under hard loads or the A/C is on? I was only planning on running one electric fan on my swap, so I'm not really sure on how to hook it up.
Thanks
Bill

Speartech

iTrader: (14)

I'll skip the whole explanation of how the fan circuit works, but basically they can come on in a couple of different combinations based on coolant temperature and A/C use.
You can use 1 fan for your swap just fine. In that case just use the primary fan wire (green) and forget the blue wire.
Actually wiring the fan relay does cause some confusion for a lot of people. The thing to remember is that the green wire is the GROUND for the relay control coil.
If you supply a "12 volt with key on" wire and the green wire to the relay coil, and a heavy gauge wire from the battery to one relay contact, and another heavy wire from the other relay contact to the fan, all will work as designed!

When the correct temperature is reached, (229 if your PCM is stock <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> ) the PCM will ground the green wire, the relay will energize, and the fan will come on!

70 LS1

iTrader: (1)

I just picked up three relays from radio shack and using the wiring diagram from the service manual, wired them to the PCM. Works great. Now I just need to lower the temp that the fans kick on. <img border="0" alt="[Corvette]" title="" src="graemlins/corvette.gif" />

Lesrace82

iTrader: (8)

are all the relays that are controlled by the computer, controlled by adding a ground from the PCM to the relays, or just the fans?

Speartech

iTrader: (14)

No and no. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

But most are.

Speartech

iTrader: (14)

No and no. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

But most are.

Lesrace82

iTrader: (8)

Guess I'm getting lost now, Im only needing two relays that I know of, one for fuel pump, and one for the cooling fans. Are the wires coming from the Pcm supplying grounds or 12 volt power?
Thanks
Bill

70 LS1

iTrader: (1)

Not sure about the fuel pump relay, but the fan relay signal from the PCM is a ground signal.

Speartech

iTrader: (14)

I fully explained the fan relay above. The PCM supplies +12 volts for the fuel pump relay.

Lesrace82

iTrader: (8)

Thanks for the replys everybody.

Boosted One

iTrader: (6)

this might make it more simple
switched 12v+ to 86 on relay, fan wire from pcm (green) to 85, heavy guage (12ga or better)to 87, and heavy guage output from 30 to fan. 87a is not used. This if for a SPDT standard automotive relay.

Frank

jeromio

Looking at the diagram in my service manual, it makes it seem like the blue wire is the primary fan and the green wire is the secondary:
<a href="http://240z.jeromio.com/motorswap/fans.tif" target="_blank">
<img src="http://240z.jeromio.com/motorswap/fans.gif" alt=" - " /></a>
(click the image for a larger, easier to see pic)

It looks like, in the stock config, the left fan doesn't get a ground unless Relay 3 (in the middle), which is controlled by the blue wire, is switched (grounded) by the PCM. So when blue is switched, Relays 2&3 are energized, providing 12v+ to the Right fan, which is permanently grounded. If green is grounded by the PCM, but blue is not, the Left fan won't have ground and won't turn on. Not sure what the White wire between relays 2&3 is for. The left fan ends up getting a reversing 12v+ which is useless since there's no corresponding ground?

Unless there's a secret permanent ground for the left fan? There's a separate description in the manual that agrees with John's explanation. This diagram just doesn't seem to make any sense.

So, I am going to use 2 relays. They'll both get the same 40amp fused hot wire. The blue wire will control the High speed relay and the green will control the low speed. I have a 2 speed Taurus fan.

I currently have just the blue wire connected to the low speed and it does turn on when the motor warms up (after about 3 minutes of idling). Doesn't really make much sense....?

LS1 PWRD

When Fan relay 1 is energized the fans run on LOW speed. White wire is used to ground fan 1 to input side of fan2 which in turn causes both fans to turn at a reduced (low) speed. When fan relays 2 & 3 are energized, relay 2 supplies 12v to fan 2 and relay 3 switches the White wire (grnd fan 1) to the Blk wire which is the true ground and both motors run on high speed.

Hope I have explained this properly. If not, fire the questions back to me. It is quite simple really. The fan motors are in series when operating on low speed and are in paralell when operating in high speed.

There is 12v being supplied to the relay coils at all times and the PCM/ECM grounds the coils through a 'driver' to energize the coil(s).

Speartech

iTrader: (14)

The diagram makes perfect sense, but why bother trying to duplicate the factory setup??
Most people have enough trouble hooking up one relay correctly, let alone using three to do series-parallel switching.

The green wire IS the primary fan. When the PCM pulls that line low, the relay energizes. The key to the primary circuit is that the center relay has a set of contacts that are closed when at rest.
When the primary relay closes, current flows thru the relay to the LEFT fan motor;

then OUT of the left fan motor thru the closed contacts of the MIDDLE relay;

and INTO the RIGHT fan motor, which is always grounded.

So when the primary cooling fan temp is reached, BOTH fans run with 6 VOLTS applied to each motor. The relays have put the fans in SERIES with each other.

When the secondary temp is reached, the center relay is energized by the PCM, and this relay is a direct ground path for the primary fan motor, so it now runs on 12 VOLTS, or high speed.

The right relay also energizes at the same time, applying full 12 volts to the right fan.

Now, BOTH fan are wired in PARALLEL (12 volts to each) and are running in high speed.

The way to fully understand what happens in each situation is to follow the current path thru EACH relay when energized and un-energized. The little arm with the arrow is what swings and directs which set of contacts the current flows thru.