A/C Fan help

[MY6.2SS]

Hello Group,

I have my LS swap completed.
I am dealing with the A/C now. I can't get the other fan to kick on when I turn the A/C on. Both fans do work.
My fan set up is this....Factory F Body fans hooked up to a new 3 relay harness. If you touch the blue or green wire to ground they come on. When you touch them both to ground at the same time both come on.
I have a "LS Harness Connection"harness. I do have the A/C request wire hooked up, it has power when I turn the A/C on.
Any thoughts ????
Thanks, David

 

[383_StealthRam]

Hi there!

You've described the issue pretty clearly, but didn't provide any detailed info on what "3 relay harness" you're using (brand, part number, etc..), or provided any pics/diagrams, etc. to provide much meaningful help. A picture paints a thousand words I always say...

Having said that.....most 3 relay cooling fan setups work the same where one relay provides for the A/C on control to enable the other two relays when you turn on the A/C. Each relay has it's own control wire (blue and green below) that also can control each fan separately or twisted together to turn on both relays at same time. Relay activations are usually seeking ground triggers. There are other three relay diagrams that are intended to provide for 2 speed (high/low) fan operation, that would be different wiring setup than the diagram below.

If you study this Painless Performance wiring diagram for their 3 relay setup, you'll see it's very simple. When the A/C clutch on wire sends power to the first relay, that then provides the other two relays a ground from it's 87 terminal, to the other two (fan control) relays terminal 85 ( the blue and green wires, one has a diode). If you see on the two fan control relays terminals 85, there is *also* a second blue and green wire that is the ground trigger that you hook up to ECM fan controls or engine temperature switch to seek that ground.

Some ECM's (like Holley EFI, or Edelbrock Pro Flo 4 for example) have separate outputs for Fan #1 and Fan #2 where you can set difference on/off temps for each if so desired. Otherwise if you want them to always run together at same time off a switch, just put the blue and green together to trigger both relays simultaneously.

Here is the link to the Painless PDF, and diagram from their kit. Hopefully this is similar to what you're using and helps you sort things out.

https://www.painlessperformance.com/Manuals/30117.pdf

Above diagram courtesy of Painless Performance. I take no personal liability, or credit for it's use here.

 

[MY6.2SS]

The harness is a brand new F body harness, from the fans to the relay ending in a ground, positive, blue and green wire. Factory.

 

[383_StealthRam]

Again, I would love to help but really need more info, what year F body harness? You said you have factory LS harness connected to a three relay fan harness. Does your three relay "harness" look anything like the above diagram? Can we get a picture of LS/harness wires? Picture of relays and wires attached? Hand drawing? Can I buy a vowel??? 🤔

The important connections are, which it sounds like you understand based on your OP.

A/C On Input wire, where is this coming from, and where is is wired to? Direct to a Relay or ECU input?
Fan 1 Relay trigger wire, where is connected to? Switch, Sensor/Switch, ECU? If ECU, what ECU and pin?
Fan 2 Relay trigger wire, where is connected to? Switch, Sensor/Switch, ECU? If ECU, what ECU and pin?

If you're running a "factory" ECU, you may need to garner help with the tune that is loaded to check on the circuit operation and verify proper functionality. For example, you may be assuming the ECU are going to command (ground the fan relays) just because you have the KEY ON, ENGINE OFF and turn on the A/C. That is not a valid test, and you may need to have the engine running, and some other input(s) to the ECU before it will enable any fan control. Like for example, A/C pressure sensor/switch input/value.

The fact that you are using THREE relays to control TWO fans leads me to believe you're just going with a simple fan turn on switch/sensor (like the diagram above) which will ground your Fan 1/2 relays, and the additional third relay is to enable your Fan 1/2 relays when your A/C is on (regardless of the fan temp switch being grounded or not).

I'll say it again, a picture(s) paints a thousand words...

Regards