Electric Radiator fan shut off to start engine when engine already warm

[Montierth]

Hi all, I installed a Jegs electric radiator fan with relay set for on 185 and off 170 and besides it being very loud seems to work very well. The one problem I have is when I am driving around and the engine is warm enough for the fans to turn on, if I turn off the engine - say to get gas - when I go to start the engine the fans are running and the engine has a hard time starting. What does everyone do in this scenario? Do you wire a shut off switch with a relay? I would hate to turn off the fans and forget to turn them back on.

[RustyPile]

Use an ignition ON voltage source to excite the fan relay. Use the temp sensor for the ground path. In other words - the sensor completes the ground circuit at 185 and off at 170...

[Montierth]

I'm not quite sure what you mean. Do you have any pics or examples. It seems like I just need a 5 to 10 second pause on the fans when the engine is warm to be able to start so fans aren't drawing from battery.

[Montierth]

One clarification. When the engine is warm and fans kick on the fans stop when I turn off the truck. But when I go to start the truck the fans start immediately to run again and draw power from my starting the truck since the engine is still warm

[Accelo]

I will see if I can clarify this.
Use an ignition ON 12v voltage source to power the relays. Then the temp probes, or ECM if you have one, grounds the circuit to start the fans. The ignition ON circuit has zero voltage when you are cranking. It only powers up after the key returns to the RUN position. Our trucks have this circuit. Maybe some others can help you identify the correct position in the fuse panel to connect this up. Or just use a light and attempt to identify the correct blank on the panel.

Modern cars have changed from switching the power side of the circuit to switching the ground side. Mainly because it makes it easier for computers to controls the circuits. However, it was used on some of the factory circuits like the dome and cargo lights even back in the 70's.
More information here;
https://www.youtube.com/watch?v=4w_8SvET7wM

[RustyPile]

[deleted} double posts

[RustyPile]

The relay draws very little current so I use the radio fuse circuit for Ignition ON power. The radio circuit is "hot" when the ignition is on, but is not when the ignition switch is in the START position..

Here's a link to the controller/relay I use.
https://www.summitracing.com/parts/der-16749


Derale says it will control 2 fans but after a few seconds of running, two fans will blow the fuse.. One of those Derale fans cool my BBC engine just fine.

[RustyPile]

You didn't say what brand fans you have. I have a complete Derale system on my truck. Derale product installation instructions are available as downloads on their website:

www.derale.com

[Montierth]

Thanks for the responses
I have the:
JEGS Dual Fan Dual 12" Diameter
JEGS Dual Fan Wiring Harness & Relay Kit 30 Amp (185° on 170° off)
AAW wire kit

It's been a year or 2 since I wired it all up. So I'll have to take a look at it and see what I did. But is sounds like I need to wire the fans to on not start. Without looking at everything and going from my bad memory it seems like AAW had a wire that was for electric fans which is what I probably used but why would it be from the Start vs On. Will look tonight after work.

[Montierth]

Called AAW and they say the Orange Electric Fan wire at the firewall is only active with ACC and On and not during start. So I will look at it tonight and guessing I tied fan relay into wrong wire. Thanks guys for all the info.