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Discussion Starter #1
Would like to install a manual override for the cooling fans on my 2007 Exige.

Searching the forum I came up with one thread where it was almost done https://www.lotustalk.com/forums/f313/elise-cooling-fan-relay-question-112899/ but this requires splicing up the oem wiring which I would like to avoid.

Can you simply run 12v from a fused ignition source thru a double pole single throw switch to the positive side of each fan input and leave the oem wiring.
Should the oem thermostat switch turn on at the same time as the manual switch they both would have the same power source, (both fans would come on anytime the manual override is on).

This method would only require adding a small pig tail two wires in one wire out at the fan itself and oem wiring would remain intact.

The negative/ground wire has continuity to the chassis continually.

Would appreciate input from electrical gurus, Thanks
 

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Would like to install a manual override for the cooling fans on my 2007 Exige.
Ron,

I looked at the schematics really quickly and the problem is that the fans are either run in series or parallel based on low or high speed, respectively. So, supplying power to just the fans is going to cause a short when the fans are in low speed mode. Not a good idea!

Later,
Eldon
 

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What problem are you trying to solve?
 

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Discussion Starter #4
Ron,

I looked at the schematics really quickly and the problem is that the fans are either run in series or parallel based on low or high speed, respectively. So, supplying power to just the fans is going to cause a short when the fans are in low speed mode. Not a good idea!

Later,
Eldon
Plan B
Add two relays just before each fan where it the oem circuit goes thru the normally closed circuit until power is applied by the added auxiliary circuit to the relay coil and looped to the NO contact. This would break the NC oem circuit and you could send power to the fans on the NO side of the relay?
 

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@Ron-323 I have to ask the same question as @glb, what are you trying to accomplish? By adding more relays in the circuit you are just increasing the possible failures that may occur and with British vehicles, will occur.

Later,
Eldon
 

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Discussion Starter #7 (Edited)
Texas heat is the problem.

Here is link to just how hot it can be on the asphalt https://www.cactushugs.com/science-temperature-hot-asphalt-insanely-hot/

I track the car and many times you can go to the grid with an unpredictable wait time with the grid temp at 100+

If you wait for the oem thermostat to kick on the fans in series the car is over 208 degrees and 217 degrees before turning on full speed and rising quickly. This means you going out on the track many times at 220 degrees and it does not cool down at high rpms and Texas heat.

You can bump the ac on and off to start the fans but this is problematic as they will only run for a short time.

I would like to start both fans at 170 - 180 and try and keep it as low as possible.
 

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Discussion Starter #8
@Ron-323 I have to ask the same question as @glb, what are you trying to accomplish? By adding more relays in the circuit you are just increasing the possible failures that may occur and with British vehicles, will occur.

Later,
Eldon
Agreed, but if the oem circuits are wired thru the NC side of the relays, The most likely failure is in the NC oem mode.
+all circuits should be fused appropriately.
 

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I think a lower thermostat temp would be a better idea
I saw a posting recently that BOE changes the temp lower which seems to be the case in my car although I haven’t heard back from them via email
My fans are on high in the 190s now
 

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Discussion Starter #10
I think a lower thermostat temp would be a better idea
I saw a posting recently that BOE changes the temp lower which seems to be the case in my car although I haven’t heard back from them via email
My fans are on high in the 190s now
I have a 170 degree thermostat installed now, but idling in heat without air movement the temps rise quickly.

I am thinking of trying the Mishimoto 155 degree thermostat - in this heat I believe the ecu 160 degree rpm limit would not be a problem.

It would be great if Boe could lower the ecu fan on temp as I have a Fastworks tune. Please let me know their answer.

Thanks
 

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Agreed, but if the oem circuits are wired thru the NC side of the relays, The most likely failure is in the NC oem mode.
+all circuits should be fused appropriately.
Ron, The failure is not that you have a short but that the contacts of the relays get damaged, which is the typical failure, and either the fans are stuck on or won't work.

Now, if you want to do this then put a relay in series with each fan. Normally closed would be OEM wiring. Normally open would be wired to 12V. You are going to need a DPDT relay for cooling fan #1 because you are going to need to switch both leads and provide 12V and ground.. Cooling fan #2 can use a SPDT since all you need to do is give it 12V. Also, do not run the 12V power for the fans through your control relay. Your control relay should just be operating the coils of the control relays.

Later,
Eldon
 

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Discussion Starter #12
Thanks so much for the input (especially EldonZ)

I have reached out to BOE to see if they would do this via my Fastworks, but they have not responded.

Here is the configuration I have come up with to install a manual override switch (all would be done pigtail style so oem configuration could be reverted easily)

Manual Cooling Fan Override Switch / Relay Configuration
Spst toggle ign switch 12v chained to all relay coils (activation)
Relays are Bosch style automotive relays 14V DC 40/30A SPDT 5-PIN WATERPROOF

Common Relay to Fans 1 & 2
Relay 1 configured NO - 12v (20amp fused) common terminal & connects to (fan1)Purple Grey Wire
& (fan2) grey wire after relays 2 & 5
Fan 1
Relay 2 configured NC - Breaks Circuit of Purple/Grey Wire from oem relay to Fan 1
Relay 3 configured NC - Breaks Circuit of Blue/Grey Wire Fan 1 return to oem relay
Relay 4 configured NO - Has grd as common terminal & connects grd to fan 1

Fan 2
Relay 5 configured NC - Breaks Circuit of Grey Wire Fan 2 from oem relay to Fan 2

Am I on the right track? Is there a better way to configure or would it be simpler just to disconnect the oem and go with a separate fan controller like this: https://www.summitracing.com/parts/der-16759
 

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At the A/C control module or the ECU, you can ground circuit 363 (Blue wire with Slate [grey] stripe) it will cause the fans to run at low speed. If you ground circuit 363 (Blue wire with Slate [grey] stripe), and circuit 364 (Blue wire with Yellow stripe) it will cause the fans to run at high speed. This is how the ECU turns on the fans when the coolant temperature calls for it, or when the A/C clutch is engaged. I've attached a wiring diagram for reference if it helps.
 

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At the A/C control module or the ECU, you can ground circuit 363 (Blue wire with Slate [grey] stripe) it will cause the fans to run at low speed. If you ground circuit 363 (Blue wire with Slate [grey] stripe), and circuit 364 (Blue wire with Yellow stripe) it will cause the fans to run at high speed. This is how the ECU turns on the fans when the coolant temperature calls for it, or when the A/C clutch is engaged. I've attached a wiring diagram for reference if it helps.
I agree with Jetblast. Grounding those two signal lines should do the trick. The ECU most likely uses a FET or transistor to pull these two signals down to ground when it is controlling things. Grounding those signals should do no harm to the ECU.

BTW. The schematic has an error by showing Control Relay contact in the normally closed position going to pin 87 of the relay. It should show it going to pin 87A. The schematic can be misinterpreted if you aren't aware of this.
 

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Ron-323, you are way over thinking the problem and solution. If you are going to use relays, only two are needed. I believe @Jetblast has the easiest and simplest solution. Grounding the two outputs from the ECU is the best way to override the fans. The only thing I would be concerned about is checking what happens if both the high and low speed are selected at the same time. I have not looked in detail at the schematics but I'm sure @Jetblast has so he should be able to answer this. The outputs from the ECU are most likely what are referred to as "Open Collector". These can be used in a "wired Or" configuration with no harm occurring to the ECU electronics.

Later,
Eldon
 

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Discussion Starter #16
Thanks so much all.

Where is the best place to create this connection to ground, or just "t" splice anywhere?
 

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The only thing I would be concerned about is checking what happens if both the high and low speed are selected at the same time.
Eldon
Selecting both the high and low at the same time isn't an issue since one of the two wires you ground for the high-speed setting is one of the wires used to trigger the low-speed. If a person hot-wired only the low-speed wire and the temp rises, the ECU will request cooling and start the low-speed circuit, since that is already running nothing will change. If the temperature continues to rise or the A/C is requested, the ECU will request high-speed and the fan speed will increase. In other words, the ECU will never notice that the system has been hot-wired and it will continue to function as it did from the factory.

And @Ron-323, it doesn't matter where you make the connections to ground the circuit, I would choose a place that is easy to get to, protected from rain or road grime, and also easy to route the wires to whatever you're using for a switch. I don't believe that you'll need any sort of relay since it should be a low-current switching circuit (the factory relays will continue to do the heavy [current] lifting). Even though it's a ground circuit, make sure to do it right, solder connections if possible, heat-shrink exposed wires, use dielectric grease for terminal connections, and secure the wiring to prevent chaffing and vibration. Good luck and we look forward to seeing your final result.
 

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@Jetblast thanks for following up on this. Since you have looked closely at the wiring diagram, does the high speed only work if the low speed has been pulled to ground first/also?

Later,
Eldon
 

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@Jetblast thanks for following up on this. Since you have looked closely at the wiring diagram, does the high speed only work if the low speed has been pulled to ground first/also?

Later,
Eldon
Eldon, that is correct, both circuits have to be grounded for the high-speed to work. The ECU will ground circuit 363 (Blue wire with Slate [grey] stripe) to activate the fans at low-speed, and the ECU will then also ground circuit 364 (Blue wire with Yellow stripe) to activate the fans at high-speed when both circuits are grounded.
 
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@Jetblast - Thanks for the clarification!
@Ron-323 - So, take a DPDT switch that is On-Off-On and you would have the choice of Slow or High speed fans with one switch. To the common of the switch, wire 363 to one set of contacts and 364 to the other set. Wire ground to both sides of the 363 side NO contacts. Wire ground to one side of the NO contacts for the 364 side of the switch.

Later,
Eldon
 
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