Cooling fan on/off

[jlfernan]

Have a MK4 complete kit. Used the Ron Francis wiring harness. The RF harness powers the cooling fan with an always hot fuse. How would one go about changing this to a keyed fuse?

[Rdone585]

Use a relay with ignition and the turn on input. It will act like a light switch for the fan. the 12 volts running to the fan will only be enabled if the key is in the ignition position. If you google for use a relay as a switch, you'll get tons of hits (e.g. https://www.electronicshub.org/what-...-how-it-works/).

[Papa]

The Ron Francis harness powers the fan through a relay. The relay is ground triggered using either a thermostatc switch or EFI control. Some also use a manual override switch. The power to the relay is supposed to be from a switched source. If wired properly, the fan won't run with the key in the off position.

[Ted G]

Yes: "If wired properly, the fan won't run with the key in the off position"

I'm actually thinking about including a switch to either leave the fan on for a bit after ignition is off or turn the fan off when I want more than 190 degrees. LOL

[jlfernan]

The Ron Francis harness powers the fan through a relay. The relay is ground triggered using either a thermostatc switch or EFI control. Some also use a manual override switch. The power to the relay is supposed to be from a switched source. If wired properly, the fan won't run with the key in the off position.

Actually the RF harness designed to run the fans with the ignition off. Would like to know how to retire the the relay to a switched fuse. You can see in the diagram that it’s powered through the battery feed which means it always hot.
IMG_0542.jpg

[Papa]

This is how the RF fan circuit is set up:



The relay (pin 30) is always hot, but the blue fan +12v wire is only hot when the relay is energized by providing power to pin 86 and ground to pin 85, which closes the switch between pins 30 and 87.

Edit:

After looking at a picture of the RF fuse panel, it does actually look like the fan relay is getting BAT FED power on both pins 30 and 86 (via jumper wire). With EFI fan control, once the key is off, the ECU will open the fan control circuit. With a mechanical thermostatic switch, the fan will continue to run until the temperature goes below the switch's rated temperature. If you want to have the fan off with a thermostatic switch when the key is turned off, you just need to connect pin 86 of the relay to a switched power source like my diagram above shows.



This is representative of the picture above:

[jlfernan]

Thanks for the help. I’ll try and contort myself under the dash tomorrow and fix it.

[Papa]

Thanks for the help. I’ll try and contort myself under the dash tomorrow and fix it.

No worries. Just be sure to tape or put some heat shrink on the other side of the cut (the one going to the large red wire). That'll be hot all the time and you don't want it to short on you.

[jlfernan]

Gotter dun! Fifteen minutes and working like a charm. Thanks again.

[Jeff's First FFR]

This is how the RF fan circuit is set up:



The relay (pin 30) is always hot, but the blue fan +12v wire is only hot when the relay is energized by providing power to pin 86 and ground to pin 85, which closes the switch between pins 30 and 87.

Edit:

After looking at a picture of the RF fuse panel, it does actually look like the fan relay is getting BAT FED power on both pins 30 and 86 (via jumper wire). With EFI fan control, once the key is off, the ECU will open the fan control circuit. With a mechanical thermostatic switch, the fan will continue to run until the temperature goes below the switch's rated temperature. If you want to have the fan off with a thermostatic switch when the key is turned off, you just need to connect pin 86 of the relay to a switched power source like my diagram above shows.



This is representative of the picture above:

The switched 12V is the assortment of BROWN WIRES. Connect the relay end of the cut red wire to the BROWN wires buss bar.
You should check that the BROWN wires is switched by the ignition switch first, just to be sure. This is what I did. This diagram shows how it is done (with a Sniper).

UNADJUSTEDNONRAW_thumb_128.jpg

Have fun,
Jeff