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How do I run my cooling fan from a switch
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Twotone77  



Joined: 22 Jul 2014
Posts: 15
Location: Watkins glen n.y

PostPosted: Tue Jul 22, 2014 1:19 pm    Post subject: How do I run my cooling fan from a switch Reply with quote

Hello I am very new to the Porsche car world in general and I bought a 1977 924 and am having problems with my cooling fan and would like to run it to a toggle switch in the cab if it is possible! Thank you any help at all would be greatly appreciated
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Mars478  



Joined: 02 Nov 2013
Posts: 222
Location: NY

PostPosted: Tue Jul 22, 2014 1:26 pm    Post subject: Reply with quote

I was just up at Watkins Glen this past weekend.

The easiest way is to simply wire the fan to the battery along with a fuse and a switch run inside the cabin. I'm sure there are much more sophisticated ways to do it but this is what I would do in an emergency situation if the car was overheating or something.

However, the best way is probably to fix the issue properly...
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Twotone77  



Joined: 22 Jul 2014
Posts: 15
Location: Watkins glen n.y

PostPosted: Tue Jul 22, 2014 1:30 pm    Post subject: Reply with quote

Yes I plan on doing this for a temporary solution do I keep it wired to the radiator switch or not? I also think my fan might be bad I have a new one on order along with the radiator and everything



And I love it hear it's a great place to live!
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue Jul 22, 2014 1:51 pm    Post subject: Reply with quote

Fix it right.
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1994
Location: Redmond, Oregon

PostPosted: Tue Jul 22, 2014 1:52 pm    Post subject: Reply with quote

Twotone77 wrote:
Yes I plan on doing this for a temporary solution do I keep it wired to the radiator switch or not? I also think my fan might be bad I have a new one on order along with the radiator and everything



And I love it hear it's a great place to live!


Why not just run it separate from the rest of the harness and just hook it up direct to a thermofan switch (replace the old one)?? My experiences with switches is that if you run a switch that is a low amp switch (and many are) insufficient for it you'll eventually burn it out and be back to square one.

You'd be better off:

- Replacing the thermofan switch (they're inexpensive and usually problematic, just replace it)
- If there is something else wrong (such as a resistor somewhere for the circuit bad) you could just hook up a simple relay, hook that into the thermofan switch and boom, running fan.

I can even make a wiring diagram for how I have mine on my project car if you want.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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Twotone77  



Joined: 22 Jul 2014
Posts: 15
Location: Watkins glen n.y

PostPosted: Tue Jul 22, 2014 1:58 pm    Post subject: Reply with quote

CorsePerVita wrote:
Twotone77 wrote:
Yes I plan on doing this for a temporary solution do I keep it wired to the radiator switch or not? I also think my fan might be bad I have a new one on order along with the radiator and everything



And I love it hear it's a great place to live!


Why not just run it separate from the rest of the harness and just hook it up direct to a thermofan switch (replace the old one)?? My experiences with switches is that if you run a switch that is a low amp switch (and many are) insufficient for it you'll eventually burn it out and be back to square one.

You'd be better off:

- Replacing the thermofan switch (they're inexpensive and usually problematic, just replace it)
- If there is something else wrong (such as a resistor somewhere for the circuit bad) you could just hook up a simple relay, hook that into the thermofan switch and boom, running fan.

I can even make a wiring diagram for how I have mine on my project car if you want.


That would be great like I said I am very new to this this is my first older car and need all the help I can get!! Thank you for the help!!
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Fasteddie313  



Joined: 29 Sep 2013
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Location: Not Detriot - NMI

PostPosted: Tue Jul 22, 2014 2:15 pm    Post subject: Reply with quote

ooh ooh ooh...


just what I need to...

im lost as to witch temp sensor is witch and where they are.. and also have rad fan problems..
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1994
Location: Redmond, Oregon

PostPosted: Tue Jul 22, 2014 2:20 pm    Post subject: Reply with quote

Quick rundown on this.... firstly and foremost, this won't work if your thermofan switch is defective (so replace it anyway). The reason I chose to do it this way is so I don't have to switch it on and off and let the cooling system do the job it is intended to do.

Secondly, you may need to test and see which is + and - on the fan, if you reverse the wires it will push or pull, and you want to make sure that is correct.

Lastly, you don't need a crazy expensive relay, I chose to get one of those relays for Halogen lights that you can get at Napa. They're like $7 and just tell them you want a headlight relay. Usually they have 2 extra areas for the lights (Labeled 87A and 87B) which means you could hook something else up to it if you ever wanted (like an extra fan).

The other reason I prefer to go this method is so the relay takes the brunt of it. Also, recommend a 20A in line fuse just to protect yourself.

The thermofan acts as a temperature sensor and closes when it gets hot enough. I chose to hook up the ground of my fan to the thermofan switch. In the diagram you can see that I either hook up the primary labeled "12+ to battery..." in such a manner that you'll either want to run a new wire, or run it off of an existing wire you know is good.

In terms of the other 12v wire that is labeled ignition or switch, this is so you can still choose how you ultimately want to control it. Hook it up to something that has 12v when the car starts and it'll act like it always does. Hook it straight to the battery and it will always be on and the fan will run whenever the thermofan switch kicks in. Hook it up to a switch and it will only run when the switch is at temperature AND you've switched it on.

Lastly, the spade labeled 87 goes to the + on the fan.

Pretty simple and basic, but since you're new to this stuff I Hope that explains a bit. The ground indicators in this diagram would be grounds you would run to the chassis. I chose to mount my relay in the engine bay next to my headlights and then ran the chassis grounds to the frame. Easy peasy, hardly had to run any wire.

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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1994
Location: Redmond, Oregon

PostPosted: Tue Jul 22, 2014 2:22 pm    Post subject: Reply with quote

Fasteddie313 wrote:
ooh ooh ooh...


just what I need to...

im lost as to witch temp sensor is witch and where they are.. and also have rad fan problems..


The thermofan switch is the huge ass brass sensor that sits in the radiator with 2 spades sticking out of it that is likely corroded, ugly looking and probably no longer working if it's from the 70s or 80s at this point (they're like $10 or $15, not expensive to replace).
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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Twotone77  



Joined: 22 Jul 2014
Posts: 15
Location: Watkins glen n.y

PostPosted: Tue Jul 22, 2014 2:35 pm    Post subject: Reply with quote

Thank you it helps a lot
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1491
Location: Not Detriot - NMI

PostPosted: Tue Jul 22, 2014 2:52 pm    Post subject: Reply with quote

aren't there 2 circuits?

a resisted circuit that works after shutdown and a full power one that works on ignition?

I believe I am only getting a reisted, on any time, circuit to my drivers side fan..

neither ever fast, only drivers slow..


and from what your satying I can go..

power-fuse-relay-both fans-ground

and then

power-relay-thermofan switch-ground

to flip the relay...

and ditch that resisted circuit, and the rest for that matter, and the fans will run full blast whenever that thermofan switch says so?

makes sense.. I think ill do it that way...

you really think you need the relay or could I just go

power-fuse-fans-thermofan-ground ??

the thermofan switch is watercooled
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1980 931S - LSD - FMIC - GTS fuel - hobby
95 M3 manual coupe - summer DD
06 X5 3.0 auto - winter DD
01 RS25 coupe - 90% Retired
06 MDX - bought for mom to DD
81 Rambler BBC 454
97 Tercel long retired/sitting
77 gs750 - 95 300ex - 89 blaster


Last edited by Fasteddie313 on Wed Oct 08, 2014 7:40 am; edited 1 time in total
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1994
Location: Redmond, Oregon

PostPosted: Tue Jul 22, 2014 2:57 pm    Post subject: Reply with quote

Yes but the way I have it hooked up it's full blast when it's on. No low speed, no resistor in line. Just on or off. A resistor in the circuit reduces amp/power and slows it down.

And yes, if you run a chassis ground to the thermofan switch, and then the ground on the other connector to the fan, when the thermofan switch gets hot, the circuit closes and grounds the fan.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1491
Location: Not Detriot - NMI

PostPosted: Tue Jul 22, 2014 3:11 pm    Post subject: Reply with quote

CorsePerVita wrote:
Yes but the way I have it hooked up it's full blast when it's on. No low speed, no resistor in line. Just on or off. A resistor in the circuit reduces amp/power and slows it down.

And yes, if you run a chassis ground to the thermofan switch, and then the ground on the other connector to the fan, when the thermofan switch gets hot, the circuit closes and grounds the fan.


nice!!!

why don't they just build shit like that in the first place...

I don't see how a bigger beefier switch in the first place is more expensive than a relay and a bunch of extra, and vulnerable, wiring...

putting a set of brand new Harley running lights on an evo sportster, it had a thumb switch and a relay and a fuse and power only when low beams were on etc..

and it was made to cheat, I took the bars off and ran the wires correctly rather that there stupid cheat wires that save the tech 15 minutes..

bunch of nonsense... to say the least I wasnt one bit impressed..

come on Harley give me a real switch...

explained it to the owner, wired it my way (with the fuse and relay/thumb switch independent of ignition period)

and got a great tip over my pay..
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1980 931S - LSD - FMIC - GTS fuel - hobby
95 M3 manual coupe - summer DD
06 X5 3.0 auto - winter DD
01 RS25 coupe - 90% Retired
06 MDX - bought for mom to DD
81 Rambler BBC 454
97 Tercel long retired/sitting
77 gs750 - 95 300ex - 89 blaster
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ksis  



Joined: 22 Aug 2011
Posts: 120
Location: New York

PostPosted: Wed Jul 23, 2014 4:45 am    Post subject: Reply with quote

The radiator in your car is from a Jeep. The thermoswitch is at the bottom of your radiator, blue wires...make sure they are plugged in. I would run two wire right to you fan to vwrify its still good. Trace those wires right back to the battery. You can tap into one of those with a switch in your dash.

Yes, this is my old car....take care of my baby....I will play the step father. Just always send me a PM so I know you posted a question.
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!tom  



Joined: 28 Aug 2006
Posts: 1869
Location: Victoria, BC Canada

PostPosted: Wed Aug 20, 2014 1:49 am    Post subject: Reply with quote

I don't understand the purpose of this approach.

You've essentially put a switch in to DISABLE the fan. Why would you want to do that?

I would have thought what would be wanted was a switch (relay, whatever) in parallel with the thermal switch. This way when the additional switch was "on", the fan would turn on (the same way as if the temperature was high), and when the additional switch was "off", the system would work as designed, where the fan was controlled by the thermal switch.

I don't like the idea of being able to disable the cooling system. Too easy to accidentally bump the switch and have no cooling.

The resistor is useful in order to limit the power being pulled from your battery when the engine is off and therefore not charging. If you want to defeat this system as well, I'd suggest the same approach again; a switch (relay or whatever) in parallel with the resistor. Therefore in the switch "off" position you won't kill your battery as much with the engine off, plus you get the benefit of running the fans at full speed when the engine is off (for whatever reason).

You could easily wire up two relays to one toggle switch to over-ride the factory system, or have it revert to the way it was designed.
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