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Old 03-17-2015, 01:28 AM   #1
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Manual radiator fan

Has anyone wired in a switch to manually operate the radiator fans? I've pulled the AC, so I can't operate that way. In grid, my car gets a bit hot and I'd like to turn the fans on much earlier than 220 or whatever temp is automatic.
I tried jumping from the relays, but no luck.
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Old 03-17-2015, 07:40 AM   #2
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Has anyone wired in a switch to manually operate the radiator fans? I've pulled the AC, so I can't operate that way. In grid, my car gets a bit hot and I'd like to turn the fans on much earlier than 220 or whatever temp is automatic.
I tried jumping from the relays, but no luck.
I have done wiring on a bunch of Boxsters and 911s of various years. Most remove the fans completely to get better cooling without the restriction that the fans add when they are not running. That said, I was also asked to add in fan wiring in a 997 race car that did not originally have fans for the reason you are mentioning.

What you are looking for would be a pretty simple change. I assume that you would want just high speed to bring down temps quickly and you have the original wiring in the car? All you have to do is install a SPST on/on switch in series with the small yellow/gray trigger wire from the DME to the high speed fan relays. In a convenient place cut the yellow/gray wire from DME to the high speed fan relays and extend what are now two wires to wherever you want the switch. Connect the wire that goes to the high speed fan relays to the center terminal of the switch. Connect the wire from the DME to the top terminal on the switch. Connect the bottom terminal on the switch to ground. When the switch is down, the high speed fans will work as normal controlled by the DME. When the switch is in the up position you will manually turn on the fans. You could do the same with the low speed by interrupting the yellow/green wire to the low speed fans.

HTH!
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Old 03-17-2015, 07:54 AM   #3
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Originally Posted by j.fro View Post
Has anyone wired in a switch to manually operate the radiator fans? I've pulled the AC, so I can't operate that way. In grid, my car gets a bit hot and I'd like to turn the fans on much earlier than 220 or whatever temp is automatic.
I tried jumping from the relays, but no luck.

Mine are wired with a switch in the dash. Center radiator doesn't have a fan but the sides do and they appear to be stock fans. I'm not sure how it was wired though - but it can be done. They are effective in cooling the car down especially after track sessions.
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Old 03-17-2015, 08:01 AM   #4
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Exactly what I'm looking for. Thanks!!
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Old 03-19-2015, 04:23 PM   #5
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im switching to csf radiators all around with no fans/no rear shroud on my race boxster
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Old 03-23-2015, 04:25 PM   #6
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Wired in a switch, fans wrk great. Thanks for the info.
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Old 03-26-2015, 05:50 AM   #7
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Wired in a switch, fans wrk great. Thanks for the info.
Glad it worked out as you wanted. It would be interesting to me to see how much of a difference in temperature it makes to leave in the fans vs. removing them. I believe the factory Cup cars, etc. come without fans, but they do have wiring there in case you want to add them.
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Old 05-09-2017, 11:26 AM   #8
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bringing this back up. Where did people tap the wires for the fan switch? It appears that the DME wiring runs down the drivers side sill.

Did you tap before you got to the fuse box?

thanks.
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Old 05-09-2017, 02:11 PM   #9
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I did this with 3.4 Box several years ago that would run a little hot at times. i just ground out the high speed relays (20 and 22) using a switch that I mounted in the back of a center console cubby tray. Worked really well. No splicing and easily reversible. There is a post on renntech.org by "1999PORSCHE911" that goes over the hack.

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Old 05-09-2017, 03:08 PM   #10
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I did something similar to what SoloPierre did.
I mounted the switch hidden from view, on the relay panel cover next to the dead pedal.
I'll post the schematic when I get home.
It's a 3 position (Off center), SPDT toggle switch. You either go to Low or High or Off. I usually keep the fans on High the entire session and during cool down.
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Old 05-09-2017, 07:31 PM   #11
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Here's the diagram. It might be the one by 1999Porsche911.
Just use single stranded alarm system wire, bend it 90 degrees on one end, and stick it in the relay socket (pin 85) then place the relay back in the socket. Then run a ground wire from chassis ground to the center (common) pole on the switch. Not the most elegant solution, but it is entirely reversible. I drilled a small hole in the relay panel cover (out of sight, cheap) and installed the switch there. Makes for short wires. Low speed relays are # 1 and 3, High speed are #2 and 4 (test to make sure).

Make sure you identify pin 85 on the socket correctly. There are hot sockets in there.


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Old 05-10-2017, 04:08 AM   #12
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nice.

Thanks guys.

I was able to find the yellow/gray wire, so I'm just gonna cut and solder in the SPST switch.

Thanks again.
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Old 05-10-2017, 05:37 AM   #13
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These fans are a popular mod lately, I am just about to finish up a similar mod:



My switch has 2 positions and just turns on the high speed fan mode.

I've got an event at Carolina Motorsports Park in 2 weeks so I will be curious to see how much this helps there.
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Old 05-10-2017, 01:05 PM   #14
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These fans are a popular mod lately, I am just about to finish up a similar mod:



My switch has 2 positions and just turns on the high speed fan mode.

I've got an event at Carolina Motorsports Park in 2 weeks so I will be curious to see how much this helps there.
Steve, I'll be curious too. For me, the benefit of the fans was on grid, and cool down. It might help some in low speed corners. I should do a run with then without to see the difference.
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Old 05-10-2017, 04:37 PM   #15
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Don't know how much this helps... it's a copy and paste from Rennlist a few years ago.


Radiator Fans

The mod consists of installing a switch that will allow you to turn on the high speed radiator fans at any time, while maintaining the automatic operation of the fans. The same thing can be done for the engine compartment fan.

Connect a wire to the ground of the 2 high speed fan relays located on the relay carrier located in the driver’s side foot well. The relays are #20 and #22. Feed this wire to where your switch will be located. Connect the wire to one side of the switch. Connect another wire from the other contact on the switch and then connect the other end of this wire to a chassis ground point.

With key on, this switch will now immediately turn on both radiator fans providing maximum cooling. When you turn the key off, the fans will continue to run for about 5 seconds until the relay shuts down. Your fan operation remains normal when the switch is off.

If you are adventurous, you can automate the operation of this switches so it will switch off at a specific speed, or operate when vacuum is present only, etc.

You can choose any style switch you want and even use Porsche switches. I simply used a toggle switch that I installed in the batwing.
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Old 05-10-2017, 07:14 PM   #16
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Just completed this mod. Fwiw you want an spdt switch with either on/on (preferred) or on/off/on.

Also, note that there are two yellow with gray wires in the bundle. One controls the comfort up windows which wont turn on your fans (yes, i know from experience)

I drilled a small hole by the fusebox for a ground.
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Old 05-11-2017, 05:28 AM   #17
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Steve, I'll be curious too. For me, the benefit of the fans was on grid, and cool down. It might help some in low speed corners. I should do a run with then without to see the difference.
For sure on grid and cool down - right now (before installing this) my driver side fan is wired to run on high all the time (I bypassed the failed ballast resistor) and when I turn on the AC on low which kicks the fan on, the temp really comes down fast when I hit a cool down lap. I have a replacement resistor that I will wire in soon because I don't want it running on high every time the AC is on.

On a track like Roebling, where there is a decent amount of WOT, but it is very smooth and flowing, I think it will help some, but I think it will really have a bigger impact on tighter more technical tracks like The FIRM, which is mostly a 3rd gear track with a lot of tight lower speed corners. I think running the fans during the session there should help out. Except for one sweeper, and a hairpin, this track mirrors my ex wife's driving style - floor it until it is time to slam on the brakes. The car heats up pretty quick at this track especially when it is warm or hot outside.
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Old 05-13-2017, 02:39 PM   #18
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Got it wired up and it works I did a little drive around town, lots of stop and go, water temp started going up (not bad, just normal.in town driving, 85'ish F oat). Turned on the fans, within 3-4 minutes it was back on the 180 line (I have the low temp thermostat)


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Old 06-18-2017, 08:03 AM   #19
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Got my manual fan switch (hi/off/lo) installed, as well as replacing toasted ballasts. I like the functionality overriding the system as needed.

My question though is that by system default the lo-speed fans should turn on at 97 deg C, suggested by the Bentley manual, but mine do not until 102 deg C. The temp reading is from the climate control hack so should be fairly accurate, as you would read from the proper diagnosis tool. Is 1997 DME programmed differently or any faults in the system to be looked at?

For now I can flip the switch when I want cooling but just wondering...
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Old 06-18-2017, 09:05 AM   #20
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I am pretty sure the low fans trigger at 102° C, and high fans come on at 110° C. However, if you have the AC on the low fans will already be running. I did not wire the low fans to a switch, because I have the AC on most of the time. I have found triggering the high fans when on city streets or rush hour traffic keeps everything nice and cool, not sure if I will bother wiring the engine compartment fan.

One question, what amp/volt rating is the minimum for the fan switch? I am not happy with the switch I bought, and I want to make sure I get the correct type. Thanks!
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