Fan 2 control

P59 computer,OS 12579405,Blue + Green connectors. Had 1 fan connected to pin 42 Blue connector,worked good.New radiator installed with 2 fans. According to Lt1swap.com,I add a wire to pin 33 Green connector for fan 2 control. When it gets to set on temp,the relay for fan 2 just clicks on and off, not turning the fan on.Fan 1 works fine.I have my wide band o2 sensor wired into pin 14 Green connector-A/C refrigerant pressure sensor signal. Using that circuit to monitor my wide band,would that mess up the signal for fan 2 and be causing the relay to click on and off.

Check your positive and ground wires. If it clicks the ecm is sending a signal for the fan 2 .

I switched the trigger wire from fan 1 to fan 2 relay and it all works as it should. The ground that works the trigger for fan 2 from the computer is on and off,should be a constant ground,not on and off.

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Originally Posted by 89 Caprice 6.0L

I switched the trigger wire from fan 1 to fan 2 relay and it all works as it should. The ground that works the trigger for fan 2 from the computer is on and off,should be a constant ground,not on and off.

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I noticed something on the forums once where some ecus fan 2 wasn't used and was set to evap or something weird. Needed to change a setting in the ecu and it worked perfectly. Once I get to a PC I'll double check

System, ac, recirculation fitted (from-ac -- to-- fan #2)

Thank You Sir,works perfect now

240sxpooter hit it on the head, had this same issue few days ago. came across this info somewhere else and now both fans work as they should. never thought to check the AC tab lol

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Originally Posted by 240sxpooter

System, ac, recirculation fitted (from-ac -- to-- fan #2)

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With this change will the AC system still work in a stock setup? Or is this for removing the AC from the engine in order to run a second fan? Thanks.

Mine was set on AC Recirc,I'm guessing try and change it and see if the recirc works.

More thinking on doing that. Before I changed the setting it was,I guess,a pulse ground making the relay to click off and on.After the change it is a steady ground. Might do something to the AC control.

GM has these set up to automatically switch the AC system to re-circulation if the pressure gets too high. By using this function to switch your fans to a higher speed you don't see such high AC pressures. You can still manually command recirc from the AC control panel in the vehicle when you want it.