View Full Version : Manual Engine Fan Switch?
Chainsaw
07-15-2022, 01:39 PM
I intend to wire the engine fan up to the Sniper ECU which should suffice 99% of the time, but I'm considering also wiring in a manual fan switch as a back-up in case the ECU befouls itself.
Is it possible to wire it this way? I can see some potential issues in theory, but I'm a knuckle-dragger, not a sparky, so I need advice. If it's possible, is it reasonable to do so considering any potential added complexity?
Jacob McCrea
07-15-2022, 02:01 PM
The Ron Francis wiring harness from a few years ago allows this by having two fan wires coming off the fan relay, and I imagine it still does. I seem to remember that one wire is intended for a temp sensor/switch in the radiator, while the other is for a temp sensor/switch at the engine. I took the wire for the radiator and put a toggle switch in it, then ran to ground, so the toggle switch functions the same as a temp. switch/sending unit in the radiator. The other wire is run to a temp. sending unit/switch in the engine.
The odd wrinkle in my Ron Francis harness was that the two fan wires were always hot, unless I shut off the master disconnect. So, when I shut the car off the fan would keep running until it cooled off, unless I unplugged it or flipped the master disconnect. It got annoying immediately so I added a toggle switch before the engine sending unit. Now I have to power up the "auto fan" sending unit with a toggle, and can also turn on the fan manually with the other toggle. Works well.
Yep. Just add a switch to ground in line with the Sniper fan control wire or off the second wire in the harness. The switch feed goes to chassis ground and output to green RF thermo wire.
Blitzboy54
07-15-2022, 09:40 PM
Yup. I did exactly what papa said. Works like a charm and very easy to do. I use the Sniper to control the fan but if it should ever fails the override is there.
Chainsaw
02-27-2023, 12:19 PM
to follow up on this, I need a trigger signal to turn the relay on and the wiring above does that, correct? Any issues with feedback into the Sniper ECU?
egchewy79
02-27-2023, 12:56 PM
no relay needed. I used the green fan wire from the front harness and pulled it out of the bundle that contains the fan power wire and ground. wire this up to a switch and ground the other side of the switch. when switch is turned on, it completes the circuit and manually turns on your fan.
Jim1855
02-27-2023, 01:44 PM
No knowledge about EFI, Sniper or otherwise or even the Ron Francis harness. I do know about heat and fans.
I would run a manual fan switch not because of potential problems with the EFI controller but simply to be able to turn the fan on prior to the engine/coolant getting too hot. This most likely happens during slow speed cruises on hot days where there's no air movement through the radiator. Think Woodward Dream Cruise or extended stop and go traffic. Getting ahead of the cooling problem helps.
Then a word to the wise, remember to turn the fan off when parked. They are really hard on batteries. I have personal experience.
Jim
Norm B
02-27-2023, 01:55 PM
The Sniper unit provides a low amperage ground signal to trigger the fan relay. If your harness does not have two wires running from the ground side of the relay then, splice into the one running to the Sniper and run it through your switch to a ground. Will not cause any issues with the Sniper.
HTH
Norm
AC Bill
02-27-2023, 03:15 PM
My fan is wired in such a way that it will turn on after parking it, and turning the engine off. Many modern cars do this. It only runs for a very short time, (maybe once or twice for 45 seconds to a minute),so there's never been an issue with the battery being drained. Having the manual switch also allows me to turn the fan on just prior to parking, so the engine is already cooled down a bit before shut down. This helps reduce the time the fan runs automatically, or even it running at all.
Norm B
02-27-2023, 04:55 PM
If you are using the Sniper to control the automatic fan function then the fan can't run after the ignition is switched off. Depending on your wiring configuration, it may be possible to turn the fan on with the manual switch.
Norm
CraigS
02-28-2023, 08:28 AM
I agree w/ Jim1855. My engine ran at 180 deg but the best sensor I could find was a 195. I know that 195 isn't going to hurt anything but...on a hot day in traffic I always flipped the manual switch. That kept the temp at 180 no matter what.
weendoggy
02-28-2023, 10:13 AM
I agree w/ Jim1855. My engine ran at 180 deg but the best sensor I could find was a 195. I know that 195 isn't going to hurt anything but...on a hot day in traffic I always flipped the manual switch. That kept the temp at 180 no matter what.
Yep, first switch flipped leaving the hot pits. Although I do have redundancy in my system with radiator switch, EFI and toggle all wrapped up in one. You know, just in case one fails. :)
sread
02-28-2023, 11:58 AM
to follow up on this, I need a trigger signal to turn the relay on and the wiring above does that, correct? Any issues with feedback into the Sniper ECU?
On the Holley tech forums discussing this subject, they highly recommend putting a diode in the activation wire leading to the ECU - just in case...
Nigel Allen
02-28-2023, 07:16 PM
G'day Jack,
Follow the drawing below. There is no feedback to the Sniper, or need for a diode, using this circuit.
180944
Hopefully this will get it happening for you.
Cheers,
Nige.
My fan is wired in such a way that it will turn on after parking it, and turning the engine off. Many modern cars do this. It only runs for a very short time, (maybe once or twice for 45 seconds to a minute),so there's never been an issue with the battery being drained. Having the manual switch also allows me to turn the fan on just prior to parking, so the engine is already cooled down a bit before shut down. This helps reduce the time the fan runs automatically, or even it running at all.
How does cooling your engine off quicker after turned off help anything? Sorry, prob a dumb question but seems like your engine will naturally cool off either way.
CraigS
03-01-2023, 08:21 AM
Some cars are wired to keep the fan going after the car is shut off. On a hot day it can actually run for quite a while, 15-20 minutes. One reason for that is everything is at it's normal temp while driving and air is flowing. When you first shut off the engine, it's temp can actually rise a bit because everything is just sitting there w/ no air flow. The concern is whether the battery can handle that fan run time and still start it next time.
Jeff's First FFR
03-02-2023, 02:04 PM
G'day Jack,
Follow the drawing below. There is no feedback to the Sniper, or need for a diode, using this circuit.
180944
Hopefully this will get it happening for you.
Cheers,
Nige.
Hello all,
I just made a little clarification to Nigel's schematic. It's the same circuit with a little bit more info. This will solve the problem. Requires a SPDT (single pole double throw switch); this will not bother the Sniper. It allows the fan to be turned on ANYTIME. However, moving the relay feed from +12 HOT to +12 KEYED will keep the fan off when the ignition is off. Cut the RED wire to the fan relay and jumper to the BROWN wire in the KEYED area of the fuse panel to do this.
Hope you enjoy,
Jeff
180997
Nigel Allen
03-02-2023, 03:27 PM
Hello all,
I just made a little clarification to Nigel's schematic. It's the same circuit with a little bit more info. This will solve the problem. Requires a SPDT (single pole double throw switch); this will not bother the Sniper. It allows the fan to be turned on ANYTIME. However, moving the relay feed from +12 HOT to +12 KEYED will keep the fan off when the ignition is off. Cut the RED wire to the fan relay and jumper to the BROWN wire in the KEYED area of the fuse panel to do this.
Hope you enjoy,
Jeff
180997
Thanks Jeff. That is an improvement.
Cheers, Nige